Better top end and comparable low end I would say, I don't think I've ever seen the engines running side by side. The 4.6 is a nice engine, for an HPI, and the V-spec we all know is a great mill. I know I'd want a V-spec rather than the HPI though, that's for sure. What makes engines better/worse is more down to the powerband, and I would suggest the V-specs powerband is more useful than the HPIs. This is mostly guesswork though...