I recently bought a Epson perfection v200 scanner since all my slides and negatives are 35mm. Up to date I've have scanned some 600 slides and negatives, some as 55 years old. At 3200 dpi grain is plainly visible in most negatives and slides, so, a higher dpi would only produce a bigger file but no extra detail. Only Kodachromes admit a 4800 dpi scanning (the maximum optical sanning of this scanner) without showing the film grain. Probably Velvia and other modern extremely fine grain films will also admit a higher dpi.