Just wanted to update this and explain a little more about the troubles I was having with this new driver.
Thanks to Thad at AJA for writing to me directly after seeing my post here on the cow.
By "slow response" the main thing I'm talking about is if I have 1 clip on Video track 1 and another above it on Video track 2, if I "hide" video track 2 to see the clip on track 1, the output of the card doesn't change. Nor does the viewer in Premiere. If I then "scrub" the timeline, or step one frame forward or back, then the output is updated, but it's not when I hit the little "eye" icon to disable a video track.
For us, this is a big deal, as we are constantly "online-ing" edits by comparing our HD conformed sequences to a low res "offline" quicktime edit, so we need to be able to make sure that we've conformed frame accurately.
To be honest, I only installed the new driver for about 10 minutes. As soon as I saw the above wasn't working still, I reverted back to 4.1.4 which works fine doing this.
Response time of hitting spacebar to play, is far better than I noticed it in 4.2 so there are definite improvements, but not having the output update immediately when hiding a video track is a show-stopper for us.