I am the happy owner of both a Steyr m9 and P99 in .40. Perhaps the caliber difference makes for an apples and oranges comparison, but I find I can empty the 10 rounds from the steyr in about a quarter of the time that I can with the P99, with better accuracy.
The P99 is extremely accurate, and both guns exhibit flawless reliability. A friend of mine can shoot the Walther much better than I can using slow fire technique. I have much better luck with the Steyr. I am able to keep all shots in about a 5 inch group firing one round per second at 20 feet with the Steyr. I cannot even reacquire the front sight that quickly with the Walther, and I have Meprolights on it (highly recommended, by the way).
Most importantly, the trigger on the P99 is horrible compared to the Steyr. The Steyr has a Glock-like trigger in that it has the same pull from start to finish, but the Steyr trigger is much better than a Glock or P99. The reason I say this is that it is much more crisp. Not as crisp as a 1911, but total trigger travel is about 1/8", which is the best I've seen on a polymer pistol. With the nearly 1/2" travel on the standard p99 in single action mode, I tend to pull about 1 round per magazine well off POA. That just doesn't happen with the Steyr. I know it is a "training and practice" problem, but a good firearm shouldn't require any special skills to shoot reliably. The very first time I pulled the trigger on the Steyr, I got a dead center bullseye. All I could do was grin and feel VERY happy with my latest purchase.
I am interested in the P99 QA. I believe that it might solve the trigger problem of the standard DA/SA gun, but I haven't had the chance to try one yet.
As far as grip angle goes, it probably depends on the shooter. The Steyr does have a more abrupt angle than any other gun I can think of, (except a Ruger .22) and in such things it usually isn't a good idea to stray far from the norm. However, I find it very comfortable. The grip is also smaller than the P99 which should make for more concealable carry. (I live in Ohio, and can't carry...yet!)
Jim