Probably not but transcoding the shot to a 16Bit Tiff sequence may help. I also often do some color correction to improve the edge behavior before doing rotobrush and I often create a Garbage Matte.
If the working time is killing you and you are stuck with your machine specs try rendering a 4K image sequence from the 8K original, then using the rotobrush as a track matte for the original footage. Scaling it up, doing a little filtering, pre-composing it, and then refining the edge matte. It should be just fine. the 16bit files will maintain the color separation, color correction may improve separation from the background, a garbage matte means fewer pixels to work with and your work should go faster.
Also, don't forget that if you nitpick every frame you decrease the likelihood of smooth transitions in the matte and the only test to see if you have pulled a successful matte is a speed full rez playback of the composite. I started my effects work drawing mattes on acetate animation frames with a paintbrush and you would be surprised how many messed up lines disappear when the composite is done and you play it back at speed. I am not advocating sloppy work, just pointing out that you can very easily waste a lot of time doing work that nobody watching the film playback at full speed will ever see.
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