I have to agree with biscuit on this one. If you want a VERY fast car either get something other than a Zed or spend a fortune on FI'ing the Zed. The Zed owns it's looks very well, it's a GT car not a racer unless you strip it out. For a medium to high budget I'd do the SC but if your budget is low you can always go for NOS. although, NOS won't give you 400bhp unless you forge the internals, then you're looking at £5k+'ish
I'm contemplating a Stroker kit for next year, this will give you a great platform for 400bhp++