I have them on my savage and love them! They're great for the track. It doesn't deter my steering too much, and I never don't have enough traction, but if I'm heading for a crash, they allow me to break traction in a controlled way.
But, I'd imagine they're not that much different from the regular bowties cept in the aspect that you're a lot less likely to roll over w/ the 40 series. I say this because the 40 series have almost zero sidewall which in theory makes them more responsive, but it kind of cancels out due to the size. Whereas the regular bowties have a bigger sidewall, but smaller size.
But I'd reccomend the HPI dirt bonz over the regular bowties...more sidewall support...
And those new HPI nubz look interesting...extra small for better responsiveness...
Nubz are not legal to race most places... I think I'm going to keep what i have (new wabash 23mm and bow ties). I was also looking at the standard size maxx wheels for the 23mm hexas and the dirt bones.