I use Blender as a video editing program and I recently started colour grading my material. Now my computer is pretty slow, for now and I want to upgrade, but I won't use Node-editor for now, so I colorgrade directly through strip-modifiers, because even with identical effects via compositor-nodes vs strip modifiers, the latter always renders faster (around factor 2-1.5). BUT, there's a big problem: In strip modifiers I can only use the histograms that the Video Sequence Editor is offering me, which are lackluster and bad. In UV image editor, via tool shelf, I have WAY better and more accurate visualizations. I have found no way to load a strip from the sequencer in UV image editing. Is there a way? Also, either histograms always get very "spikey" as soon as even the slightest modifications are applied.
On another note, why does using scene strips from Compositor eat up so much more processing power than using video clips directly, EVEN IF the node editor doesn't actually apply any changes?
And finally: I currently have a GTX660 and a 3.75Ghz Intel and want to upgrade to a better Graphics Card. I really DON'T want to stick with Geforce. What's a good card on a 300-400€ budget that will give me decent rendering power for 4k videos? Currently render 30 frames per minute, while normal FHD 1080p material does 130-210 frames per minute with equivalent modifications.