Just to put my bit in. I have a Epson V500 too and I scan at 300dpi but set the size of the print I wish to make in the drop down menu. But set one size larger.This doesn't waste any time/effort in scanning and as 300 dpi is what I would use for printing (Not that I do a lot of digital prints anyway).
I don't think I have ever used a scan of 6400 it just takes too long. I did the same thing when I had a Nikon LS5 film scanner but that was a different ball game anyway.