Sorry for being kinda afk. I'll clean up the vapoursynth assistant more soon, but it more or less works now.
I've tried NNEDI3 and fast denoiser with a test video recently, and I can tell you that neural network upscaling + KNLMeansCL or V-BM3D for temporal denoising looks WAY better. And it shouldn't be too slow with a good GPU.
Also, when you say NNEDI2... are the source clips interlaced, or did you just mean NNEDI2 image doubling?
Yeah, NNEDI3 (I meant that version) would be meant here for image doubling. At its time, it was the best scaler by far, and it yielded some very light denoising and great antialiasing as a side bonus. And it was developed with neural networks.
As for M(V)Degrain3, it's just the latest motion compensated denoiser I know of. It is quite slow (much more than, say, dfttest) and at its time struck a great balance between denoising and actual detail removal. Where can I read about KNLMeansCL and V-BM3D?