Wow. You've got at least 10 tracks on that sequence! Cool editing, and I love what's showing in the scopes for the current view ... but honestly, for this many tracks, this intensive of work to do ... you'd probably need a bit more machine tuning to get it to run smooth.
Just saw a bit on the hardware forum, for a lot of the i7's the recommendation is to get them up to 4Ghz via overclocking if possible, that helps the CPU start sending more to the GPU. Intriguing, that. Next ... DDR4 memory has a higher speed than DDR3, and has the same effect as lifting the CPU to 4Ghz ... better GPU performance or at least, utilization. For your perusal & consideration?
And yea, for your work, that GTX 680 might do it with the above changes, or ... might not. Again, I'd check the tweaker's page:
... and the Hardware Forum.
Neil