I would stick with the VF series ( VF30 or VF34 ) over the SR40. The SR50 is another story, but might be too laggy for most people. In the dyno's I've seen, the SR40 doesnt make enough power over the VF34 to warrant the price.

IMO, I would try and get ahold of one of Forced Performance's 18g's. Mine cost $799 which is still cheaper than a VF30, VF34, or a SR40. Even a 16g turbo which you can now get from a number of sources is superior to a VF34/SR40.