Your instinct is correct here: you should be scanning to get as much detail as you reasonably can from your negative. With most dedicated consumer film scanners that should be between in the 3000-5000-ish range.
By the time you get to your final print size, you want around 300 dpi if you can. As it happens, at this density, a 14-inch-wide print would work out to 3000 dpi from a 35mm negative (uncropped).
Silverfast may be assuming that you're printing at the same size you scanned - eg, if Silverfast is driving a flatbed scanner and you want to make a copy of what's on the platen.