senwar said:
My opinion is you don't like the car you currently have for whatever reason that may be.
I feel that too.
t20alu, you keep comparing it to the Astra VXR, which 'beats' your Z4... and/or comparing it to other cars purely on a road speed metric, despite you being fresh and new to the car where it will always feel slow until you get into the groove with it. In pure performance terms an Evo VII or even a Civic Type R would leave a Z4 for dead on most roads with a good driver, only a very good experienced driver would make use of the Z4's potential, if at all, on the road. The appeal of the Z4 should come from more than comparisons with hot hatches or rally reps etc
You have modded the suspension with cheap aftermarket springs possibly making it less nice before you even know what it's like normally. That could well be a problem now without you even realising it

It could well be that the suspension and RFT's have just compounded the problems which makes the M Z4 stand out so much better. Revert to OEM, ditch the RFT Bridgestones, and see what you think
Personally I think you have got a lovely example of a Z4, in a nice colour combo! I'd leave it alone otherwise you'll hurt it's resale value, and learn to enjoy it for what it is!