SVP works via Avisynth.
If you "disable it in ffdshow configuration by unticking it" then SVP is NOT working.
If video is lagging with SVP on then you probably should adjust something.
I didn't notice much difference in quality after disabling it but if you say so...
Also, might as well mention that i noticed the same issue when SVP wasn't running and disabling avisynth also fixed the lag.
Not sure what i can try, i'm starting to dislike MPC more and more so will probably try with another player soon.