I can't speak at all to the P99 question--never fired one; never even held one perhaps. But someone mentioned reliability concerns with the SW99, so before we scare you away from an excellent piece, let me pitch in.
I bought a new SW99 in .40 when the model first came out. Immediately after purchase, I rounded up 14 different ammos and fed them all through with no problems. Now, something like 3500 jamless rounds later, my Smith still looks new, fires accurately, and is my primary concealed carry weapon.
Three things I would change: (1) Mag capacity. Mine are ban-era tenners. New 12s would solve that. (2) Size. It's just a tad big on my small frame. In the future, I will look to something that hides better on me. (3) sights. I just don't care for three dots of the same color and size. Call it a great personal inadequacy if you must. I prefer Glock sights. Or maybe I just need to shoot more often, which would be a pleasure with my SW99.
Anyway, don't let 'questionable reliability' stand in your way without a good, solid source for the concern. For whatever 5000 rounds are worth to your peace of mind, my experience with the Smith has been impeccable.
Oh...and I LOVE the ambidextrous mag release! In fact, I like every lever on the Smith better than every lever on my Glock G20. So handy, so painless.