During cold weather, almost none. It all depends on your end goal, and other factors come into play. Top speed? Probably what I have now or even longer, given enough room. Acceleration? It depends on how sticky of tire you want to run, and how long you want to make the bike. I have a pretty sticky tire, but not a slick, and my bike is about 8inch longer than stock.
My builder is about 220lbs, and he has very bad traction problems with my bike, My weight actually helps with traction, but it obviously hurts me once I have traction.
If I would of built the bike to be a drag racing bike, it would have an even sticker tire, and at least a -1 front sprocket, assuming I could keep the front down at that point. But I wanted a crazy fun street bike, my goal was to be able to go WOT in 2nd, and keep it down. Assuming its about 60* outside, I can do that just fine. So the gearing is perfect for what I want it to do.
I mainly say stock gearing, because usually people gear their bikes like crazy, and say "Yea I had it up to 180mph" when in reality it was like 150 on a GPS. So right now my bikes speedo is only off as far as Kawasaki allowed it to be, when they made the bike.
