Will that much weight affect how the bike handles? Definetly. But when you're not packing you won't even notice the rack weight.

My choice for that much weight would be to put it onto a rack. I've gone grocery shopping and loaded about 20 to 25 lbs into my backpack and grunted it home up the hills around here on a regular basis but it's not a happy riding time. If it was on the bike it still wouldn't be a happy ride because of the way that much weight makes the bike feel sluggish to turn but at least my back wouldn't be getting poked by tins and carrots...