hughes torque converters? ts

so what is the big difference between 10" and 11" any why, I have a **** stock one in now, is carp, burned up. trans toast. building a new transmission, using GOOD parts in it!!! that is why I'm looking into converters. want to do it only once. what do you guys mean by tight? slip is bad on trans builds too much heat, and kills fuel mileage. want to apply when driving down road/freeway, and not slipping burning things up, that is what happened to the a999 l/up that was in car, and couldn't cut the mustard to the new engine. @ 300-350 hp, never dynode.