I would say that they are both around equal. For single core performance, an 8350 is probably equivelent to a sandy-bridge i5, so the 4670 will beat it. In terms of multi-core the 8350 will win. To be honest though the difference is usually miniscule, they are both great CPUs. What I would look at is what else is important other than gaming power.
If you want cooler temps, lower power consumption and the upgradability the i5 is for you. If you plan on doing multiple heavy programs at once, e.g. playing and recording gameplay, the 8350 is most times better.
Also if you do any photo-editing, video-editing or other computational heavy applications they normally utilise all the 8 cores so the 8350 would out perform the i5, even giving an i7 a run for its money.
Another thing is cost, I can get a 8320 (an underclocked 8350 which is virtually identical) for about £110 while the i5 is closer to £160.