Looking at your hardware, you'd benefit from a CPU upgrade, especially if you play WoW as it's extremely CPU dependent as more people are around you(assuming you're not GPU bottlenecked). Your GPU won't bottleneck an upgrade either (compared it to one of my 570's, which I used for a few years before going SLI)
Your mobo supports the upgrade as well.
I'd go with an i5-2500 (at least), essentially any socket 1155 CPU that's at least a 2500 Sandy Bridge.
Your mobo doesn't support Haswell procs, and they're basically the Sandy Bridge replacements.
It's up to you,
This is what you can expect
http://www.anandtech.com/bench/product/289?vs=288
Your resolution won't matter that much, as long as you're not running above 1080p.
Even if you're not playing WoW you'll benefit from the upgrade, quite a bit too.
It's up to you if it's worth the cost though, since you're paying quite a bit more than others due to your location.