Here's a price comparison between the RB6 and the B4.1WC (which was the current kit at the time of the Rb6's release):
Rb6 - $450
TOTAL: $450
VS
AE B4.1 WC - $250
AE Big Bores - $100
Alum. Wheel Hexes - $17
Alum. Steering rack - $20
TOTAL - $367
Your talking a $83 price difference between the two.
However, I would say the b4.2 is a good value, It's $279 pre-order price tag at Amain is pretty good since you now get all the hopups.
B4.2 PREORDER
edit: Glad to see OP made up their mind. Good luck!