So, after a long time planning and aquiring the parts, I finally fitted my Bilstein B12 Pro-Kit suspension and the M3 subframe bushings.
Why did I choose these modifications for my car ? My goal is to have a no-compromise street car with maximum drag racing abilities and acceptable tracking abilities. So I need as much grip as possible, and wheel hop minimization/elimination. Also the suspension should not be much stiffer than my current M-Sport suspension. And the whole thing should be reasonably priced.
From my research, I concluded that monotube dampers (as opposed to the stock twin-tube dampers) provide superior grip by being very responsive and having the ability to damp even the slightest wheel movements without any delay, keeping the tires in contact to the ground longer. So I needed monotube for my setup. But most monotube dampers are included in expensive coilovers, and usually the coilover springs are very stiff because these are designed for the track. But I don't want to compromise the street manners of my car, not even one bit.
So Bilstein B12 Pro-Kit, at 550EUR ex. VAT, was my suspension choice.
Driving impressions (with my 17" Run-Flat winter tires !):
I really can't believe how good this setup is. It's like 10 times better than my (ok, 40.000 miles old) M-Sport suspension. I expected it to be stiffer, but in fact it feels much softer around town ! The potholes are handled incredibly well, the car seems to float over them. The M-Sport was crashy and it felt like crap over potholes. In corners the car seems flatter, but I didn't really have the chance to test this ability yet.
Ride height has changed only slightly compared to my former M-Sport suspension, I will let it settle a few days and only after that I will post a picture. It should come like 10mm lower in the rear and 15mm lower in the front compared to the M-Sport.
About the M3 subframe bushings: right now, around town I can't say I feel them. I do feel that the entire car seems very SOLID and composed, maybe they play a role in this. I really hope these bushings, combined with the monotube Bilstein dampers will improve on the wheel hop tendency. But it's still winter-like temperature outside to do any kind of test. What I can say is that there are no extra vibrations/harshness transmitted in the car with the M3 subframe bushings, even with run-flat tires.
Overall, I am extremely happy with my suspension. I managed to actually greatly improve the street manners of my car, while adding grip and sportiness. I was under the impression that any aftermarket suspension is some kind of compromise between performance and street suitability, but it seems that it isn't so.
My only concern is that after I will switch to the summer non-RFT tires, the suspension will feel too soft. I really hope it is not the case.
I will report back in a few days with more impressions especially what it's like to drive on this setup with non-runflat tires.
That's all folks !
EDIT: Some pics of the setup below.