Well you have a pretty good setup there for a bit. If I was going to upgrade things than I'd look at:
* z68 based mobo to get Quick Sync (not gaming improvement, but overall improvement for encoding)
* 2500k for the CPU upgrade, not that you don't already have a good CPU, but just saying.
* 6950 - 6970 GPU upgade(s), depending on budget.
* SSD only if you want faster loading times, your 1 TB HDD would do for most things anyway.
* Upgrade your monitor to 1920 x 1080 at least, this will give you more to work with and also take advantage of your current X-fire setup.
Currently I think you have a decent setup, so not sure if your currently having issues, but most people would like a similar setup to what you have (minus maybe the 6770's in X-fire).