question about switching gears?

now that he's said this, i'm questioning not getting the ford...he said that 3.10 will kill my low and and i won't even be ablle to burn out....i'm wanting a good street strip mtor, he said a 3.50 (ford)...or 3.55(mopar) is the one i want..but he said it would cost less to just buy one complete the way i want it..but that'll take forever to get right size and gearing etc etc