Nemo, I have both an iPF5100 and an iPF8100 and the quality of black and white output is superb. In my opinion, you are going to have a difficult time nitpicking the quality of output between all of the big printers on the market. Most of the differences are going to be with usability and other unique requirements you might have, such as onboard profiling (HP), gloss enhancer (HP), no switching of black inks (Canon or HP or new 7900/9900 Epsons), etc etc.
On my Canon printers, I have nice custom profiles created, and I just send my toned black and white images straight to the printer as a color RGB file. No 'advanced black and white mode' or anything like that. These B&W modes are nice, as they can help create rich blacks, but it is black magic and isn't ICC compliant. A black box that you have to fiddle with to get the results you desire. This isn't a big deal if you are just using one paper, but if you print on many different surfaces (like me), you will see huge density shifts that are difficult to predict.
QuadTone RIP is a great option on Epson printers, as well.