I won the Legacy Challenge yesterday with Grixis Delver, 75 can be found here. I copied a Bob Huang list a couple months ago and replaced a Price of Progress with the Flusterstorm before the challenge. I ended up going undefeated in games until game 2 of the finals vs Egget on Red Splash DNT. My actual matchups over the event were

2-0 Bryant _Cook on TES
2-0 ItsUnfair on Miracles
2-0 JPA93 on Sneak and Show
2-0 Gul_Dukat on Grixis Delver
2-0 viscoulius on Eldrazipost
2-0 Egget on Red DNT ( Magus and Direfleet Daredevil MB)
2-0 exSIN on TurboDepths

Top 8

2-0 ruckus-mh on Sneak and Show
2-0 kentaro_hokori on Grixis Delver
2-1 Egget on Red DNT

Fortunate that I didn't get any real tough matchups like Lands, the most difficult being Egget. Direfleet Daredevil is the real deal, I don't know if it will be enough to shift the core DNT build to RW over Mono White but there is certinetly a lost more incentive to do so now. Not particularly spectacular went down for me, they were typical enough Delver games, and those where the gameplan broke down, the power of patience and Gitaxian probe got me there. In particular, game 3 of the finals I kept a 7 held together by a Grim Lavamancer, t1 probe to see Path STP and Orzhov Pontiff all ready to take him down. But since I knew that I was able to grind through the removal with a Delver to soak up 1 and a Pyromancer + Therapy to get the last 2 and a creature I can't remember. I also had a nice g2 win vs Eldrazipost where he was able to cast and resolve a Newlamog with Chalice on 1 and Sphere on board.

I liked the Flusterstorm well enough, but more for Miracles / 4c Control than combo itself. I have a pretty stock 7 in 7 out against all Combo decks, so the Flusterstorm had the potential to be gravy there, but some of those 7 are lower impact than others so it still made a difference. Other considerations for that slot were a 2nd Grudge, a Dismember, or 3rd Surgical. I evaluated my needs based on what sideboard games I find myself wanting more cards to bring in, not necessarily what my worst matchups are. For example against Miracles I want to bring in more cards than I want to take out so thats not a matchup I'd want to add a sideboard card specifically for. For DnT I feel like I could always make room for more hate. But Grudge is fairly narrow in application where as Flusterstorm is potentially live against many medium matchups so I still went with it to see how it would go, and I didn't hate to see it (unlike the Liliana the Last Hope I tested, the matchups I planned to use it in, I ended up not really wanting to cut anything for).

I'll answer any questions about the challenge or my general play of the deck, though I'm sure most of you have more experience with it. I started playing it exclusively early December and have 236 match results recorded, but most of that is learning the play of the deck and sideboarding strategy with what I have, not any real evaluation of the card choices of the deck. That 1 sideboard spot is the only card in the 75 I've done any experimenting with.