Having been through the same, I can tell you the best solution is to clean the tracks and re-grease the tracks with the Honda High-Temp Urea grease. Like your car, my windows were so slow I was genuinely worried that something serious would break. From the sage advice I received here, I did the cleaning and regreasing as all is now well.
If you need the urea grease, contact Tim at Ray Lacks Acura www.hondacuraworld.com. Many here have sung his praises and I, too, am one of them. Tim can find virtually anything for your NSX. Not only is he pleasant and knowledgeable, he has very reasonable prices. I've purchased from him numerous times and have been extremely pleased.
While you're at it, you may want to buy some Shin-etsu grease to lubricate the seals around your doors so that they remain pliable. Tim can get you some as well.
Below is a link to a YouTube video that nicely shows the speed of what I believe a well-maintained (and possibly new..or relative new) NSX-R. If you watch at ~0:28, you will see one of the drivers roll-down and up the window. I know it isn't scientific, but it is helpful. From this snippet, I was able to gauge what is a reasonably "appropriate" window speed.
http://www.youtube.com/watch?v=eV_M9pxPKxg
