Treasure Trove + Gardens
Even by itself, this is decent. Open Silver/Silver, get a bunch of treasure troves, then buy gardens while flooding your deck with cards from TT. I haven't tried this with a simulator, but I think it's roughly on par with Gear/BM. If you have the time, it might be worth picking up a province, since 8 gardens with 50+ cards and a province beats 7 provinces (and a duchy). A decent source of +buy (or banquet) would definitely help this, though it might also enable a gardens rush, which would likely beat TT+G as it's fairly important to pick up the treasure troves before the gardens with this.
Banquet + IGG
With banquet, it's not too hard to buy an IGG every turn from turn 1 until they run out. At this point, you'll hopefully be at a point where you can hit 5 on most turns to rush the duchies (or better yet, gardens).