> And these settings cannot be simply used in SVP code.
SVPcode uses the very same video profiles as SVP uses for real-time conversion.
You can define your own custom profile for encoding with the settings closer to Interframe's.
> is it legal to use latest svpflow plugins in the SVP 4 directory?
yep
> If so, is there new feature/performance/quality increases?
not for Avisynth plugins