Yeah, I've just checked 2.6 alfa3, and confirm that simple script with only LanczosResize() is 1.5 times faster with 2.6.
So the simpliest solution for you is to unpack (not install) 2.6 and place it's avisynth.dll in MeGUI folder.
And SVP will not work with this 2.6 version cause it lacks MT functions.
