Personally I like the MD Sat option, well you know cause my Sunday's are limited. You might lose some people, but you might pick up some non-racer types who will take advantage of the long weekend. Maybe even get some out-of-towners coming to visit if word can get out somehow. Seriously, who actually goes away on MD weekend, unless you've got a cottage in the Hamptons. Everyone wants to stay home and relax.
If it's a choice between JH and 6P, I would race 6P. But I don't think it helps anything to have 2 local mtb races in the same day. Take that with a grain of salt from somebody who didn't do any H2H races this past season.