I have the 3 gig GTX580 and am digging it though it wasn't easy getting here. I got that vid card specifically because of Vegas but after installing really didn't see that much of an improvement. Somewhere along the lines things went fubar. For a good while I had some issues with Vegas 11 and was getting horrible playback from the timeline. It would start out at about 17-20 fps but after a few seconds would begin dropping frames further and would quickly fall to under 1 fps. Essentially it made it impossible to edit. If I clicked anywhere in the timeline there would be a good 5 second lag before that frame would show up in the preview window. I'll also add that the playback problem was happening even if I told Vegas not to use the GPU in the options. This would happen even in a new project with just one short clip, project matching the media, no effects etc. File types also appeared to be irrelevant. Even if I prerendered the one little clip it still suffered and would crawl along at under one frame per second. During all of this another thing I noticed was that V11 was opening really slow and when it would first come up it would kind of stall and parts of the interface were blocks of white for a few seconds before it would "pop" and open up fully. If I clicked on the interface before that "pop" it would say "Vegas is not responding", it wouldn't crash fully though but would just hang for a few more seconds and then finish loading.

Eventually I realized that the GPU was not being used by Vegas 11 for timeline playback despite it being chosen in the options however it was being used for rendering. I had been trying to figure out what was going on for awhile now, tinkering here and there to no avail. Finally the other day at my wits end started using an axe instead of a scalpel. Didn't go quite so far as to do a clean install of Windows 7 but got pretty close! It took a good few hours of uninstalling and reinstalling Vegas, Magic Bullet, a few other Vegas plug-ins, uninstalling anything else that was video related like DiVX and other random programs/codex, updating drivers, doing rollbacks on Windows Updates, System Restore from various points, running several anti-virus and malware programs, cleaning up hard drives, cleaning the registry, reboot reboot reebot etc etc etc. The good news is SOMETHING worked! I'm now back to 23.976 playback in most circumstances and with the GPU monitoring widget I can tell Vegas 11 is now using it for timeline playback. The bad news is I have no idea what finally fixed it, in the melee I lost track. That said all the simple things that were the obvious stuff to try I had tried before and they didn't make right whatever was wrong. By that I mean just reinstalling Vegas 11 or updating drivers, you know, the usual stuff.

Upshot is I'm just tickled pink that its working right now, opens quick, totally responsive, no lag and 23.976 playback, loving life again. Been without further issue for a good week or more now. My suspicion is that it was something outside Vegas that was messing with it and that what was happening in Vegas was more a symptom than a cause. I can only qualify that by saying the majority of changes I made during that last round were outside of Vegas. Early attempts assuming that it was exclusively a Vegas/GPU problem didn't manage to flush it out.

Not sure this will help anyone or not, if I had known that I was actually going to fix the problem I swear I would have paid more attention! I was hesitant to post this as I don't have a solid solution but seemed to me that it would be worth sharing for anyone who is having similar issues. Hopefully they'll take better mental notes than I did and come up with something more specific.

- Ray
Underground Planet

P.S. Didn't realize this was such a long post till I posted it! Though I suppose adding this PS just made it longer, okay, my bad, shutting up now.