I agree with everything eric said. I have the 7800 and when using some of the better B/W papers in concert with Advanced B/W mode, the results are striking.
The other thing to keep in mind is that Epson has about 10 years on its competition, which if I was looking to buy now would be a determining factor. Give Canon and HP a few years to work out the kinks. It'd be fair to say that 4 years from now, that experience gap will be a moot point and you'll be able to achieve excellent quality regardless of the manufacturer.
I recently saw Photographs by the Score
at The Art Institute of Chicago. The main gallery space had a mix of silver gelatin and archival inkjet prints which I was able to closely inspect. After viewing/comparing the values between an Imogen Cunnigham silver gelatin print and an archival inkjet print by Dawoud Bey, it became clear to me that digital B/W has quickly approached (and in the case of these two prints, surpassed) the tonal range of silver gelatin prints.
It's a wonderful and exciting time to be a photographer, to say the least.