We bought a new 135 in late January to replace my wife's 328 coupe.
As noted, it is a lot of fun, but certainly no CaymanS in the handling department, not to say that some modifications could not bring it closer.
It is a blast to drive though. I find it is a cross between the 06 CooperS I had before the Cayman, and the E46 Dinan 330ci we had (I'll call it an S1 with Dinan Sway bars for simplicity), although with a lot more power. We have the paddle shift automatic, and while I have not driven a PDK car, this automatic is a great "street" automatic, and I am going to have to autoX it once this year just for kicks (although I know it will understeer like a pig).
Obviously, being a sedan, it has some practicality that the Cayman simply can not have, and is certainly a bit more civilized for a daily driver / commute car, particularly with the auotmatic. Not to say the Cayman is not a great daily driver as well, but in the daily "grind" of commuting, there is a lot to say for having a car with a bit more comfort.
In short, would I give up the Cayman for the 135 - no. If the 135 would have been available with I bought the Cayman, would it have been high on the list and given a lot of consideration - yes; if you throw $10-$15k of Dinan or TC Kline, etc. mods on a 135 and get it up to 400+ HP, with thier handling tricks, I think you would have an incredible car for less money than a new CaymanS, but again, it is no Porsche.
In short, love the 135, and love the CaymanS. I guess the best decision, is to simply have both!!!!!!!!!!!!!!:banana:
Regards