V-Spec wont keep up with the motor that the factory guys have. The motors they have are worth about $1000 alone and unless you modded that v-spec it just wont match up. I know motors not even 15% of how fast your lap times are but if your going top of the line especially racing in pro ranks you need everything you can get. http://www.sigmatrading.com/RBConcept/rbpricelist.htm I don't have any other info but theres a pricing on one of the factory engines. The motor might be specifically for one road... but I'm sure the buggies don't get much or any less.
1005-RC 950.00 Rody Roem Modified 1005-C TEAM Engine

Even though I love my kyosho I'd run the XB8. Like I've said a few times before it has so many adjustments to dial in your setup perfectly and really help you find the grip and balance where you need it again especially for pro ranking stuff. The hyper of corse is no slouch but most racers like something with more aggressive handling and a lot less weight. The hyper is a full pound heavier than any other top of the line kit out there. This really hurts your acceleration and braking distance.