AndreaMG
I don't think using MT() in conjunction with SetMTMode() is a good idea. The script is already parallelized by some number of threads set in SVP.
If I put it before the frames will be on the other hand sharpened before the doubling?
yep
I thing the results should be visually the same
not really cause interpolated frames are always a little blurred
but I'm not sure if someone could really notice that 
Is it correct in my case always force it to use 8 cores?
nope, in this case CPU won't use all it's power if it'll be needed
though it doesn't matter in case of DVDs
