The Hauppauge MVP software renders pretty simple screens which require quite a bit less CPU power.
GB-PVR's screens are much more complex and use advanced features like anti-aliasing etc (and few resize transformations). Also, the GDI+ library GB-PVR uses for doing all its graphics is well known for being slower than the native windows API. That said, on a fast machine there is very little difference in response time, between GB-PVR and the original software. What spec CPU have you got in you PC?
Also, use the 'minimal OSD' option to ensure things stay responsive when viewing video.
Intel®
Pentium® 4 CPU 2.80GHz
2.79GHZ 2.00 GB of Ram
Don't worry sub I love Gbpvr, it is not a matter of complaining, don't want to give you a wrong impression, just curious. Its plenty fast enough, I guess I was wonder why? I guess now I have an answer. Thanks Sub. I guess curiosty killed the cat.