You won't notice a difference unless its in reliability!
I personally HATE having to drop the tank for any reason, let alone to change out the pump. When I put my TPI togeher for my 78, I decided to go with a heavy duty external pump instead of an 82 sending unit with 85 pump.
Mine sits on top of the frame next to the tank on the passenger side. I have never had a problem with it mounted that way- even on 110 degree days in Kansas! I change it out every three years just to be safe and it takes less that 15 minutes!
Unless you are trying to keep its stock..... go with aquality aftermarket pump thats a frame mount