I ride a bike that weights 35 pounds with all the stuff i have-- fenders, pump, lock, tool kit. I have an upright riding position and i don't go really fast-- gearing is 46:22 which is low.

When does weight become more important than riding position? For example, I read someplace that after a certain speed 75% of your energy is expended overcoming wind resistance. Not sure if I remembered that right or not. But I'm cruising along at 10-12 mph on my bike in an upright position with low gears. Just how much would it benefit me to replace my heavy metal fram with an aluminum one and reduce my total weight from 35 pounds to around 25-27?

I do think dropping 10 pounds off the bike would make it easier to move in and out of my apartment and manhandle it etc, etc.

It depends on how "hilly" your rides are. If it's flat weight doesn't matter as much.
Joe

On flat ground, your bike's weight simply does not matter at all. Gravity is what you have to fight when going uphill and ten pounds extra is significant, but it won't utterly transform you performance.

10 or 15 pounds is a pretty big number if you're talking about steering, accelerating, climbing, etc.

On the wind resistance front, it's more complicated than a flat 75% rate. Wind resistance actually increases with the square of your speed. It sounds like you have a pretty classic "postman" posture, maybe slightly less upright.

I'm out of town right now so I don't have access to it, but Bicycling Science covers it pretty thoroughly. Anyhow, if your wind resistance is x at 12mph, when you hit 24mph, it's going to be (24/12)**2 or 4 times as great. I do recall that even at relatively low speed, a postman position wastes a significant amount of energy.

I'm leaning towards an aluminum cruiser frame or an iro highlander frame/fork.