Edd,
good question, and by the sound of it, the poly's are a bit extreme. I don't have experience of poly's but my impression would be that they are likely to be harsh.
I only have refurb'd M030 at std ride height, and previously std 1986 turbo experience, so what would I know! I don't want to pretend to be any authority on the subject.
The point about stiction / movement is interesting, - because we want accurate location and also movement from the bush, and the OE fit bush allows movement but compromises location, the poly bush provides un-compromised location (excepting rose-joints) but perhaps the suspension design intent does not suit this hard unyielding material when it comes to movement.
With Hard spring rates on slicks and in a track situation where the car is set up like a Kart, the Poly's are likely a good idea.
Over pot-holes and thousands of road miles where comfort is desirable and you cannot use the last 20% of the handling envelope very often, the polys are perhaps too extreme.
Interesting too that EBC use standard bushes, (and that they have no choice) but they know a thing or two about set-up of these cars. I would put your question to them?
One thing I would not do is mix soft with rigid bushes, it could result in un predictable handling in certain situations.
Got any ARB plans? (968 M030 or weltmeister have good reputations)
Also, ride height will be relevant, I'd have similar plans to your one day and I reckon -24mm would be good with KW and 968 M030, and a Promax setup. (more helpful than CG IME)
Keep us posted
Thanks
george
944T