+1 I would love to get a pair of G Semifasciatus.
I got 2 female Watanabe (roughly 2") in Nov or Dec 2007 and the male is easily 6" now. Got 2 female Bellus (2" & 3") in Feb 2008 an both females are aound 3" and 4.25". I think you should be fine with 2 small Bellus for a year or so b4 moving them to a 180.