I almost never use the 48 that I have now, only on big descents. I can spin fast enough in the 36 - 11 to do 25 mph, on a slight downhill I use the middle for long flat sections.
I'm more worried about losing the low end because of my knees. I climb most of Diablo in the second or third lowest gear. And that's just about the same gear ratio as I'll have with a 33 - 34. I've tried climbing in my middle ring. And I can do it. But the joint pain after isn't worth it. It's a genetic biomechanical thing - my sisters have it too. I figure if it doesn't cause me joint pain, it's worth the weight savings and the added speed I should pick up, just from being in a bigger gear.
If it doesn't work out - I'll have a compact double for sale.
V.