1,
you already have fx-6300, so going to fx-8350 or even its factory overclocked overpriced version fx-9370 won't do you no good. Or better to say - you will not notice any difference.
i5 - is way better in all aspects, gaming, productivity, etc... The only drawback are resource heavy apps - like video reencoding, virtualization, etc...
so, bottom line - what do you do mostly>
- do you take, cut and encode your own videos? - if it is unbearably slow, go for the 8350, if not, oc your fx-6300.
- play games, browse the net, etc...? - i5
2,
fx-8350 should fit in the same mobo as your fx-6300. i5 needs new mobo.
if you change your MOBO, then you should do a clean reinstall of your os.
3.
personal opinion:
if I would feel limited by my cpu, i'd get the i5 /+mobo, +better cooler/.
if not - i'd put the money into a single better gpu /since I don't like sli/cf - too much hassle with both of them/.
then get an ssd, more ram, better sound card, decent speakers /or some cans/, keyboard, mouse...
rinse and repeat every year...