Have you test drove both yet?
M2 will be better if your tracking it more, but you also wont feel disappointed while at the odd track day in an F. And 2 track times in ownership isnt a lot.
As Chris Harris says when comparing the GSF vs the M5 Comp, The F car for normal british roads lets you put down more power, and feels much better to drive. Granted the GSF and RCF are different cars as are the M5 and M2, but they both hold many similarities, that may be a review worth watching as its a comparitive review video of two cars similar to the ones you are contemplating, may give you some insight.