I'd start looking at making it lighter if I were you, they're heavy cars anyway and just by putting a few carbon parts on it I'm sure weight can be saved.
That way you get a better power to weight ratio, breaks won't need to work as hard, be better handling, etc so lots of birds - one stone
I wouldn't say the Zed is the most tunable car. I've looked into it sice I got mine and I'd say £ for £ you don't get much power gain on the money you dish out compared to say the old cosworths (cos I see you're a ford man in a past life - good lad btw!).