Okay, did some testing last night and the C-class is much more competitive than the B-class. Professor, I'll update my first post with the real build tonight, but here is what I remember.
BUILD:
Upgrade to Street Engine: Exhaust, Fuel, Ignition, Cams, Engine (all else stock)
Upgrade to Race Handling: Race everything, except street weight reduction
Race Tires: Firestone (worst racing tire), one upgrade in tire width, one upgrade in tire size, Enkei Wheels
Forza front/rear wing, and aftermarket side skirts and bumper (can't remember brand, but same on both and is only option for bumper so easy to identify)
C550
Anybody want a G33K Racing Beetle (looks like geek squad), just let me know.
Coming soon to a Xbox near you!