I don't want to spam this thread, but maybe others have similar difficulties, so I don't know any better place yet to post.
Anyway, I switched the last (good) hboard to the other two that didnt perform so well (16gh each), and the magic happend: 60gh coming out of these babies. Nice. Same settings for the first 32 chips (with autotune off, I tweaked it a little bit last night, but with not too good results). The third board is autotune on, performing 17.452GH/s, 19.9GH/s, 23.336GH/s. Still some more tweaking to be done, but I'm fine for now

Also I received another starterkit for my friend (who somehow managed to go on vacation) and plugged those two right into the first mboard. Working fine: 24.796GH/s and 20.845GH/s
Update:
3 Hboards, 1 mboard. swining between 60 and 65gh as seen here
http://eligius.st/~wizkid057/newstats/userstats.php/14cbUKDLpZPJUMfr3DcKWZXmiaQRYpaZbd