Op, you do realize you'd probably see a good boost by adding the gtx 970 correct? Also, have you overclocked the 8320? I've got the older 8120, mine was stock at 3.1ghz, and I've been running it for a good while at 4.2ghz. You might reconsider getting the 970. I do realize intel has the better performing parts now, but the other thing to keep in mind is AMD is set to release a new set of chips next year. They are claiming a 40% jump. So my strategy is to wait and see if Zen is really as it's advertised and to see how big of a jump there is and possibly save my pennies for an upgrade then.
*Edit* I'd started to write this then had to step away, and finished it later, realized that you'd already posted. I would say though that you might be advised if you have not already, grab a cooler like the cooler master hyper 212 evo, and overclock the 8320 for all it's worth. That should help ease any potential bottlenecks.