With a 5D Mark II and a 1:1 magnification, you're capturing 4000 raw SPI. Perhaps more pertinently, you're capturing somewhere in the neighborhood of 60-70 lp/mm with good contrast, depending on lens. So you're essentially matching the Coolscan 9000, which rates around 67 lp/mm.
BTW, 60 lp/mm requires 3048 SPI. I think your math is off somewhere. 1600 SPI is only enough to resolve 31.5 lp/mm, and that's in an ideal world.
Anyway, given that color negative film doesn't have much contrast past 70 lp/mm and few LF lenses can achieve that, I'd say it's enough. But if it isn't, or you shoot fine grained B&W, just wait a year or two and upgrade the camera to eke out more resolution. That's the good thing about a generic rail system. Not good enough? Just wait five minutes.
The Epson doesn't really compare. In no way does it deliver 2000 high contrast samples per inch. But even if it theoretically could, that only works out to 40 lp/mm. Scanning on my 4990, I maybe see 30-40 lp/mm, but they're very mushy low-contrast lines. After some very destructive sharpening, you can bring out that level of detail, but you'll bring out plenty of noise and sharpening artifacts as well.