With stock I'd spend so much time grinding, shimming, and polishing to make the car more efficient. The b5m seems like it fits together much better (fresh molds?) from what I've seen, so maybe this is less necessary.
Honestly, it has to be pretty overwhelming to the guy moving up from the novice class to find out what measures some of the 17.5 guys are taking on their cars. Slipper eliminators, lightened outdrives, pucks, ceramics, ti screws, and so on. By contrast in 2wd mod you can pretty much throw a box stock kit out there and your success is up to you and your throttle finger. It's the driver's class.