I hit for two hours yesterday morning and played doubles for two hours yesterday afternoon. The 99S is a great frame for me. While others seem to like it strung according to Wilson's range, I find it is really nice in the high 40s. I do string my own.
One other thing to note. If you string your own, undoubtedly you've noticed you're throwing away about 6' of string with every 40' pack. This racquet is built for reels! You can probably cut quite a bit off the cost of stringing by finding a string you like that comes in reels. While Luxilon claims they designed 4GS for the 99S, you notice they didn't put it on a reel!
Wilson Steam 99S poly Luxilon 4G 1.25 @ 45