I remember some time ago spending hours researching the forums and the web in general regarding switching with the E90's.
Cost was an issue when that time came to choose (and sad to say cost would be even more of an issue now!).
320i with Sportpack, so if memory serves correctly 225/something/R18 in front and 255/35(i think)/R18 at the back.
To do all 4 tyres in one go - just under R20 000. Several posts on this forum dealt with the issue and there were many recommendations to look at Hancook V12's - it was getting the most mention and 'satisfied' feedback on this specific point of debate. All 4 tyres, just over R8 000.
Harder ride and cost aside, I would easily go with RFT's, there's a huuuuuge convenience and safety benefit in being able to drive some distance in-spite of a puncture. I remember for example being stuck on the N12, reduced to 2 lanes with their neverending roadworks, concrete barriers either side, and the pressure warning light coming on. How much of a relief it was that I could drive happily to a garage, happily continue my journey. And even if things go really wrong while you're driving - you're nowhere near as likely to lose control of the car - watched a 5th Gear test on youtube where they basically deflated, stabbed, drilled and just downright destroyed the tyres on an E90 fitted with RFT, starting with one wheel - and zooming around to feel the difference - then 2, then 3, then all 4 wheels flat, and they concluded though you could feel a difference, you could still comfortably completely control the car.
Simply put, I don't believe they last as long as normal tyres. When the tyre pressure light goes on and you have RFT's, peace of mind and safety may be a guarantee but your stress levels also skyrocket wondering if whatever's wrong can be fixed or if the tyre will need to be replaced -they're less likely to be repairable... The biggest problem is cost. The other trade-off's on choosing RFT's in my opinion can't compare with the luxury and safety of being able to continue your journey, especially in this country.