I have the stage 3 and wish I had gone 4. But the 4 had just come out and I wasn't jumping on it not knowing what kind of numbers the ported heads and bigger throttle body would put out. Seeing the numbers now, made me wish I had. Stage 3's typically pull 115 tq and 105 hp. I've seen stage 4's in the low to mid 120's.
What cams are you running? If you've got milder cams, the upgrade to stage 3 OR 4 may be underwhelming (from what I understand).
This could be right. Friend of mine rode his buddies new Stage 4 build and said it was barely noticeable over the stage 2 he had in it before. For the money he was disappointed.
I Talked bikes with a guy on the Road, I had a stage III and he had just got talked into taking his III to the IV when it came out, he was putting it back to stage III to get his Torque back where we ride. Otherwise he was happy with the IV when winding it out.