Even though the card isn’t a Adobe supported CUDA card, you can try to toggle Colorista to use the GPU instead of the CPU – it is under “options” at the end of the effect list. I don’t know if Colorista can only support certain graphic cards, so it may be greyed out for you.
Having said that, even though I have a GTX 285 in my MacPro – a card that is pretty highly benchmarked with Colorista – I find the process to still be pretty sluggish within Premiere. I, like you, struggle a bit with a workflow that allows me some flexibility after doing a color grade.
My current workflow which has allowed things to be somewhat speedy is after locking picture, I select all of the clips in the timeline and paste them into a blank composition in After Effects which matches my footage specs. This gives you one layer for each clip in your sequence. (If you have a very long sequence with lots of cuts, you may want to break this up into multiple comps) Most of the transitions and effects that you add in Pr make their way over to AE. (Warp Stabilizer will not, forcing you to re-analyze, but if you had put a colorista effect on a clip in Pr, it will show up in AE) Then, in AE you can do a color pass – denoiser, colorista and unsharp mask, etc – with a much better and faster interface.
Then, you have 2 options. You can go back to Pr and import that AE comp as a Dynamic Link, and add it to another video track in your timeline. The benefit here is that if you do have to make more color changes, you can work on your AE comp and have it update live in your sequence. But, the downside is that Pr will not playback in realtime (most likely) and the preview render can take a very long time, depending on your sequence length, codec, etc…
Or, you can render out of AE and import the file into Pr. You will have your color baked into the sequence and won’t be able to dynamically change it, but by rendering it in AE, you can leverage multi-processor rendering. It will be much much faster to see it play back in realtime. But, looking at your computer specs again, I think that may be moot. This is more important when you are running on a MacPro with many cores.
So, the summary is that Colorista 2 is slower in Pr than Ae, but you can give a try to processing using the GPU option, if available.