What does that even mean? Most people use the word "stable" to indicate a system that isn't crashing, so I am assuming you mean your computer is crashing more often with those drivers. I haven't seen a video card driver related crash in YEARS, and even when I overclock too far worst case is a "video card driver blah blah has failed and restarted".
"Not as stable" seems to imply that even with the "good" drivers you are crashing. Sounds like there is some serious problem with your computer if you are having stability problems. It should be rock solid, we aren't using Windows 95 anymore random crashes should simply never happen.
I don't think my current computer has ever blue-screened, not even once, and I've used every possible driver with my 7970 and overclocked it to 1212mhz until the driver crashed.
That I have seen, I think it was in a game of league of legends. Alt-tab out and back in and it was fixed though. Not a big deal, but I'd like it to never happen.
Unstable as in the video driver (not the system) crashed a handful of times within a 2 month period, graphical anomalies in games, and the fan speed ramp not working correctly with the WHQL drivers. The system itself is 24/7/365 stable and I brutally test any new system I put together. The system is fine and the video card was to blame period. This is not a new system, it's just a new video card, and the system has been rock solid for nearly 2 years now.
In contrast, nVidia drivers didn't crash (again, video driver crash, not system crash) but maybe 1-2 times in 1.5 years with my old GTX 570 and have yet to crash with my new GTX 680. There were also WHQL drivers available for the GTX 680 on release day. After a couple of weeks of gaming on the GTX 680 with various games, I have yet to experience any issues whatsoever.
I really don't care how good AMD's video card performance is anymore. Their drivers suck ass (I don't care what anyone says at this point...they do suck ass) and AMD apparently doesn't want to or can't afford to devote the proper amount of resources necessary to support their flagship card. When I spend $600 on a luxury product, I expect it to work and work well. AMD dropped the ball plain and simple. nVidia products only in my systems from here on out. I have absolutely no patience with products that don't work as advertised. I don't want to troubleshoot and tweak a computer endlessly. I want to play games on it and have fun. nVidia products allow me to do this without any extra effort needed, aside from maybe tweaking the driver settings from the control panel or in-game.
If I sound bitter, it's because I am. I spent $600 on a product which didn't live up to my expectations, and lost over a hundred dollars sidegrading to a product which does meet my expectations.