IMO 6 butts on a 22 should be no problem. I have done 3 8lb butts on my 18 just on the top rack. The trick is to stand them on their end (vice laying them flat on long side) and kind of form a teepee. So I'd think 3 per rack on a 22 should be pretty comfortable. 8 I am not sure, but you could always add a 3rd rack without too much work.
Kg