Great to see you doing well with the Grixis version!
I'm a recent convert to FoW. I originally started on a version with 4 Thoughtseize + 3 Inquisition. Then went URW with 4 Silence until just recently switching to Forces + counters. I think the main reason for FoW is to double as an answer to early permanent-based hate like Chalice, Thalia, Trinisphere, Cage, etc. or faster combo decks, things we may be too slow to stop with Spell Pierce or Thoughtseize on the draw.
Silence effects are strong. With 4 main, I had too many hands with 2 Silence (redundant) wishing one was a counter. It's dead in some matchups G1. 3 seems right. I think both of them are on 2 Chant + 1 Silence main plus FoWs.
When I played with discard, I liked these perks:
-perfect information to plan when and how to go off
-fills GY early
-doesn't have to take mana on the combo turn
But overall I didn't like being in black. How do you beat early permanent-based hate? Splash 4th color? RUB struggles to answer artifacts and enchantments without white or green.
Btw Surgical isn't that good against us once we go off. We can escape LED before they get priority so they can't target it, we can escape BF in response to Surgical (always have UUU floating), or we can just escape a cheap counterspell (Pierce or Pact). We can also win without LED (Petal + BF loop), without BF (Tome Scour or Grinding Station), or without Wish/Thassa (BF beats most decks). The deck has flexible ways to adapt.
Extirpate demands Silence, but Surgical and Faerie Macabre are dodgeable.