Excellent review. I can vouch for 4.5/5.0 players as many are using this around here. For the record, I'm a 54-year old 4.5 who plays mostly doubles now and hits/drills more than he plays.
To add my 2 bits, it you currently use poly in an 18X20 string pattern and break strings, this racquet is definitely not for you. If you use a 16X19 string pattern and use poly and break strings in under 5-6 hours (or any time you feel borderline too soon) this frame is definitely not for you.
My experiences echo yours directly. I was most surprised by 1) volleys are this frame felt more solid than any I've used in quite some time -- almost like a wood racquet at net 2) serves are way better than I've been getting, almost on par with the K90 I used for 6 months, 3) service returns are really smooth once you make a little adjustment and 4) my topspin backhand is killer both down the line and crosscourt.
I think this frame will help me recover some of the racquet head speed I lost since I developed tennis elbow. (My strokes have never fully recovered) While my arm feels great now, the pain way back has caused me to adjust in a not-so-good way that resulted in my drop from 5.0 to 4.5. I do not expect to get back to 5.0, nor do I want to at this point, but strictly from a playing standpoint, I would love to start hitting the ball like I used to again.
I should also note that I have always really, really liked open pattern frames way more than closed pattern and this frame is about as open as you can get so it's really up my alley.
So the guys who break poly in under 2-3 hours in an 18x20 shouldn't even enter the same room as the 99S? That's disappointing!