Thankfully I installed the RC and my Safari is back to working fine - and so far there seems to be a lot less CPU spikes and odd behaviour so fingers crossed!
Yes you're right you could do a full format and reinstall from recovery - you can also download an IPSW restore image for the system - i'm not up to date with how you run those now though, I played around a lot more with Intel machines than the AS ones so I don't know the procedure to run that image, though i'm sure I read something about perhaps needing two Macs and putting it in recovery mode. So booting to the recovery partition is definitely the easiest way still.
