The SP-1 is basically a Vibe in a MILSIM shell. If you want to improve the guns performance, drop a GOG G-1 stock board in SP-1. It's a direct replacement for the one you have now, still shoots 11 bps but gives you two modes you dont have, PSP and Millennium. PSP is 3 shots in semi then ramps up to 3rd burst every time you pull the trigger, then resets to semi when you let off the trigger for a few seconds. Millennium is similar, but ramps up to full auto. The cost you ask ? About 30.00 shipped to your door. The Fasta may keep up, not sure which one you have, but I know the Halo Too will, thats the one I use. Plus, you can pick them up used for approx 40.00.
Until I got my Axe, I used my SP-1 in this setup for awhile, now it's my back-up/ night scenario gun.