My experience with an S-PVA panel is that it looses dark clarity when looking straight on. As in, I was in the dark background of a picture and I could barely make myself out. Until I looked at it from a slight angle either left or right. It bugged me enough to return the Gateway FPD2185W. It was a great monitor, good colors (in my opinion), but that bugged me too much.
This post at [H]ardForum has some nice pictures at the bottom.
(I'm currently looking for an I-SPS panel, and I've narrowed my search to the Dell 2007WFP and the NEC 20WMGX2.)[/url]
Oh, and as far as response time varying from the I-SPS and the S-PVA, I couldn't tell you. Sorry. (Although I would assume that the I-SPS would be a little slower, if any at all.)
And about scaling, nVidia's drivers should allow you to set scaling as you have said in the Display Properties. Something about scale with aspect ratio, maybe. This laptop screen has "expand while maintaining aspect ratio," which it wouldn't do on the Gateway when hooked up via VGA. I haven't used an nVidia with a widescreen, though.