Epsons Sure Color (P600, P800, P5000-9000) have much better MK black than Stylus Pro series (x880, x900), IMHO better thank ipf 6400 (I was to go with ipf6300, but finally chose P800).
Sure Color MK can achieve density levels on standard fine art rag papers comparable to Epson Hot Press paper on x880, that was specifically designed for Stylus Pro inks.
ipf is similar to old Epsons in MK density on fine art media. Pro-x000 are much better (denser).
Sure Color MK on Hot Press is outstanding (unfortunately, paper just discontinued), can get even L*=12-13
Historically, HP had the best MK, then Epson, then Canon (in reverse for PK). Today, differences are much smaller. Try to make sample prints before deciding. I love ipf for PK look, but not MK.