Which OEM tyres did you try Shooter?
I think the factory throw on whatever comes to hand, or is cheapest that week... I drew a set of Yokohamas, which I like. At least, once the fronts had worn in a bit and lost their bite... it oversteers a lot less now - you might even describe the handling as 'neutral'
That said, having somehow got 10,000 miles out of the rears (and with tread left!) I'm changing them for a new set - it'll be interesting to see if the power oversteer becomes stronger.
I suspect the car is quite sensitive to changes (to say the least!)
Gareth, I'd talk to Richard Thorne who did Shooter's suspension setup - he was extremely helpful when I spoke to him... I don't doubt I'll work my way towards a similar setup - 19s, reset ARBs and the revised spring/damper setup.
Will