The difference between the V500 and V600 is small, I can't even remember what it is nor is the difference easily found on Epson's website. One site mentions that the V500 scans one MF negative at a time while the V600 scans 3.
I bought the V600. Btw, scanning at 300 dpi is widely considered to be the optimum for scanning prints, less will not get all the information, more is just wasting space.