weight is jsut a number. my "heaviest" weights change all the time. it's all relative to your body and your current workout.
its about flexing the muscle and getting blood in it more than just duplicating a motion. that said heavy weight is important, but the idea is to lift as much as possible without breaking solid form. there are times you can cheat a weight but thats the exception not the typical rule.
"Abs on a skinny guy are like big boobs on a fat chick - they don't count." -Shelby Starnes