Puzzled here...... the Epson V330, as shown in that video that OldBoy links to, seems to show a slide holder with four spaces for slides (quite big, for different slide sizes up to medium format), for scanning at 4800dpi. The
Epson V500 also has a slide holder for only four slides at a time, but in this case it's at 6400dpi. By the look of it, though, it doesn't do 36 at a time..... or am I missing something? The
Epson V600 - more expensive again - also seems to have a holder for only 4 slides.
So they all scan four slides at a time.... your decision seems to be between 4800dpi and 6400dpi and/or the energy saving features. The 500 and 600 also (in the specs) bundle PS Elements - but not the latest version.... certainly worth a check - the 500 actually says it bundles PS Elements 4...... which is about five years old.