360 CS or bust. Whoever thinks this is the 996 of the F range clearly hasn't experienced it...
Would a 430 be even better? Hell yes, but with every generation the price goes up $30k or so. The 355 can be a straight swap for and M3 money wise, but the fragility and maintenance costs may negate any costs advantage over a 360.
So if I am to live my Ferrari fantasy, the lowest rung I would jump on would be the 360.
2004 Z4 3.0
2014 X1 28i ED
2015 F80 ED in June