Wow, 300bhp! Not bad gains considering everyone says these cars are not great for tuning.
With regards to the GT thing.... I'd be looking to remove the seats for some decent buckets anyway... do the breathing mods, new wheels and enjoy. I could do most of this on the budget I have anyway, if I buy an s2000 I will have little left over after the hefty insurance premium. Must be honest I did fall in love with the s2000 on a test drive but I couldn't help but feel like it was a bit to impractical and expensive. The Z is certainly not a bad compromise.
I found the s2000 cabin to be really tight with not much room and im about 5ft10 so not the biggest person but it felt like there was no room to move. the handling was superb and I love the high reving engine but I missed the torque that you get with the v6. and also my mate in his s2000 couldn't get away from me on the bendy roads so id say the zed was a better all rounder that can show more nimbler cars that it can still put up a fight . also left a Scooby sti on the bends but I think that was down to the driving