IMO, having taken both cars out on the track a couple of times, the Z is OK but it's not as fun as a VX. That said, I would rather eat a VX than do any serious mileage in one, it's a complete pain in the butt (literally) on the motorway, whereas the Z will eat long distances no problem, and still be massive of fun on the twisty stuff.
All in all if you're going to do track days regularly I'd get the VX, otherwise I'd get a ZED.