Don't know about the scaling as such. AFAIK, if you exceed the capacity of the VRAM by a combination of high video settings and Screen Res then I suspect CloD gets the data from elswhere, maybe Page RAM or the HD which I suppose would cause stutters, etc. Some one else is probably better at answering that question.
What I do know is that with everything at max and within the limits of the available VRAM fps drops significantly on my system probably because of the CPU speed and everything processed by one or possibly two cores.
Finally, I promise I won't interrupt your JU88 sorties again!