Hi Wayne,
The acceleration has to do with hardware resizing. Both HDV and DVCProHD reduce the resoluton of the captured footage when capturing it from the camera head. Of course when you are looking at the footage on your HD monitor it has to be scaled back up to it full resolution. A capture card can do this one using its onboard hardware (Kona)does or it can delegate it to your CPU(some other cards).
Because the Kona uses its onboard hardware for these scaling tasks there should be more cpu throughput left over for realtime effects. This should be especially true if you were working with multiple streams of HDV or DVCProHD, or a least that is the rationale.
Hope that helps,
Gary