Big starters, small gainers
Seems that the larger someone starts out with, the less they gain. I see guys who start with 5x5 and get to 7x5.5-6 all the time but I never seen anyone start with 8x6 (like myself) and get to 10x7.
For example, look at MagnumXL, he started at 7x5 and is as long as me and has .6 inches in girth on me and we started at the same time.
Seems that God has created a sort of checks and balances for PE.