The re-circ valve is basically just an uprated part, because the OE one can fail. I did notice a much better response on gear change, as it directs boost back into the turbo keeping it spooling, where the OE one doesn't. Mine came with two springs, and you can request one for stage 3 power if required.
I run the standard cat and exhaust on mine, with just pre-cat down pipe, can made 10bhp extra from it, so with sports cat, you should see a decent increase, but would benefit further from the full system.