I use the Bogen 3021BPro too for my Hasselblad, and I use the 488 ballhead for it; it works quite well and is pretty rugged, and more importantly, cheap! My guess is if it works for a Hasselblad it'll work for the SQ; I think the weight is probably the same.
If you have the money though, the Arca B1 really is the best. I used one for my 4x5 and then my Hasselblad for a while; it was simply a dream. I only sold it because I needed money (poor college student... of course if I were poor I couldn't afford a Hasselblad, but seriously, all my money goes into photo equipment!) and also because it's a precision instrument, so it wouldn't take a beating as well as the Bogen head could, and if the Bogen head broke, it wasn't too much to replace (about $80.00).
A salesman at Keeble and Schuchat Photography in Palo Alto told me that the Giottos ballheads were just cheap Itlian knock-offs of the Kaiser ballheads, and weren't worth looking at. Of course, if it works it works, I just never tried them out.