I've been playing RUG in leagues the past two weekends. I believe I've had 3 4-1's, 5 3-2's and 2 2-3's. Good not great. I think RUG is definitely the best tempo deck in legacy. I'm trying to sort my thoughts here. I feel if I can figure out a few tweaks, those 5-0's are within reach.

Current list:

4 Delver of Secrets
3 Tarmogoyf
3 Hooting Mandrills
1 True-Name Nemesis

4 Brainstorm
4 Ponder
3 Mishra's Bauble

4 Lighting Bolt
1 Forked Bolt
1 Dismember

3 Stifle
3 Spll Piece
4 Daze
4 Force of Will

4 Wasteland
3 Flooded Strand
3 Pollute Delta
2 Misty Rainforest
3 Tropical Island
3 Volcanic Island

2 Abrade
1 Ancient Grudge
2 Grafdigger's Cage
2 Surgical Extraction
3 Pyroblast
2 Spell Snare
2 Winter Orb
1 True-Name Nemesis

I just don't think Nimbe Mongoose is very good anymore. Winter Orb is good in the same matchups. Hooting Mandrills is bigger, has some kind of shroud, gets around Chalice of the Void, isn't stonewalled by True-Name Nemesis... the list goes on. Hooting Mandrills is definitely the best creature in the deck after Delver of Secrets. It's very difficult for me to imagine not running it.

Mishra's Bauble is a poor man's Gitaxian Probe, but it's been pretty reasonable. It grows Tarmogoyf past Gurmag Angler and excelerates your Mandrills. Obviously it doesn't flip Delver of Secrets, but you can scry the top card of your library in conjunction with a fetchland or check the top card of your library and know whether you want to burn a Brainstorm to flip your Delver. I used to not like running Gitaxian Probe and Dismember in the same deck because of all the life loss, but obviously that's not a concern here. 2x Dismember is definitely a much more reasonable option than with Probe builds. The next marginal option is Preordain. I find Preordain to be a lot worse than Ponder and not growing Tarmogoyf past Gurmag Angler is definitely a tactical shortcoming. Cycling into Brainstorm, Force of Will, Wasteland and creatures for free while giving some information on what the opponent is playing seems to be underrated given that I'm literally the only person runing Mishra's Bauble in a tempo deck in Legacy.

Matchups:

BR Reanimator:
This match up has been pretty 50/50. It really comes down to the die roll. Being on the draw game 3 is pretty unfortunate. This deck has me considering Leyline of the Void.

Dredge:
Dredge seems to be making a reasonable showing on MODO, taking advantage of people Surgical Extraction only as their graveyard yard. I switched from 3 Surgical Extraction to the 2 Surgical Extraction/2 Grafdigger's Cage split to help combat this, sometimes it's still not enough to beat a broken draw.. People sure have improved the decklist, does anyone remember when Dredge used to run Deep Analysis? I'm considering Leyline of the Void.

ANT:
This can be a touch match-up, it depends on the opponent. They can definitely trick you by going off with Empty the Warrens when you're holding up Force of Will for Infernal Tutor. Seems to be matter of how good the pilot is. This is a matchup where I like Surgical Extraction, it's great to at least get a look at their hand when going off so you know what to counter.

Sneak and Show:
I guess feel slightly better agaisnt Sneak and Show than ANT. Pyroblast is certainly much better against Sneak and Show than ANT and they can't surpise Empty you.

Lands:
Lands seems to be reasonably favorable. Sometimes they just have broken starts, but if your Force of Will their one good spell they aren't doing much. Surgical Extraction and Winter Orb out of the sideboard are great.

BG Depths:
This matchup seems to be reasonably favorable. The combination of Wasteland plus counterspells plus clock seems very hard for them to beat. Mulligan for Wasteland or a hand that has good shot of finding Wasteland. This is one of those matchups that make me glad I have Abrade in the sideboard because only some builds run Pithing Needle.

Eldrazi and other Ancient Tomb decks:
These decks all seem to be pretty favorable. The combination of fast clock, counterspells and Wasteland seem to do it. I definitely wouldn't want to be running Nimble Mongoose against these decks.

Miracles:
This deck definitely crushes Miracles like it's supposed to. Miracles is mostly air these days, just kill them quickly. Winter Orb is obviously a house out of the sideboard. I like bringing in Surigical Extraction here.

Grixis Control:
This matchup unfortunately seems to be less than 50/50. I think figuring out a good way to beat Grixis Control is the key to unlocking the metagame. I board out all the Bolt effects but keep Dismember. I board in Ancient Grudge, Winter Orb, True-Name Nemesis, Pyroblast and Spell Snare. Winter Orb is always a blowout against Miracles but is only good is some situations against Grixis. When they win, it's usually a combination of Baleful Strix and Gurmag Angler. This matchup makes me want a second Ancient Grudge in the sideboard and Sylvan Library.

U/R Tempo, URG Tempo, UBR Tempo:
Every other tempo deck I've played against is slower and plays worse cards. These are all very favorable. Unfortunately, people don't seem to be playing them as much.

Death and Taxes, Maverick:
Death and Taxes is the metagame whipping boy, it only beats bad decks in the metagame. I guess it's pretty good against RUG, but the matchup doesn't come up too much and they can have problems against a strong hand. Maverick seems to be more of a mainstay in the metagame than Death and Taxes. I ended up cutting the second Dismember for a Forked Bolt and cutting the 4th Tarmogoyf to move a copy of True-Name Nemesis from the sideboard to the maindeck which gave me room for 4 graveyard hate spells. I won the one match I had against Maverick with this change in place but its definitely a rough matchup.

So I would like to work out a configuration that can beat Grixis Control. Sylvan Library would be good there and Mishra's Bauble is much better with Sylvan Library than Gitixian Probe because no life loss. Winter Orb would be the cut for Sylvan Library, but I would miss the Winter Orb effect against Lands. If had Nimble Mongoose to beat Maze of Ith, I would feel better about cutting Winter Orb, but Nimble Mongoose seems to be terrible. Surgical Extract is probably the better against Lands than Winter Orb, but I'm considering cuttign Surgical Extraction for Leyline of the Void. Perhaps accepting a worse Lands match up is the way to go.

I also want to run the 2nd Ancient Grudge in the sideboard but Abrade really is effective. Abrade is the best artifact removal spell agaisnt Maverick where it isn't clear how many aritfacts they might be running. Decks like UR Delver are sometimes running Ensnaring Bridge these days. I definitely like having extra removal spells to bring in against Elves.

I guess I'm going to jam a build that runs Leylines and Sylvan Library and see how it goes.
//End Rambling//