Thanks for the detailed reply.
I have heard a lot about "CM", a friend of mine has used it several times before on an older Samsung device - but he also mentioned bugs, or strange "things you have to do on each boot" which put me off.
With what you've said, would you recommend holding off for now until they stabilise a version? Is there any stable AOSP ROM on 4.1+?
Edit: After further research, it seems flashing these custom ROMs gives more problems than benefits. Every one I've come across has numerous posts with "accepted bugs". I'd rather have a working phone than some sketchy ROM built by a teenager! Nevermind, TouchWiz it is
You've got to really
hate TouchWiz to put up with a custom ROM, surely?!