Having driven both the B5s and the original YZ2 I can say the yz steers better and has higher corner speeds in its near kit form. However, the associated suspension absorbs the jumps better IMO, and it generates way more grip stock so it's a pushy setup from the kit settings.
If these new B6s can come close to the YZ2 in cornerspeed and still jump and generate grip better they will be on my short list to buy.
Having ran a lay down tranny (yz2) for over a year now I can definitely see the benefit of two seperate cars for high (B6C) and medium to low grip conditions (B6D).