Nah man your not bottlenecking the 7870, the i5 is way more than enough to handle the Video card. I use a 2500k which is just like .5ghz faster and use 2 6950's which is alittle faster than a 7870 and im good. you could pair 2 7870 or 7970 with any i5 and not bottleneck
No you're fine with a 2300, and Ivy is not much of an upgrade over Sandy, my vote is to forget about it. Haswell will be out next year and on a completely different socket with no backward compatibility. Save your money, you 2300 is good enough to get the job done.