I tried 64 lb in the 99S last night and did notice it was notably "harsher" than at 59 lb.
However, I also switched strings from Lux 4g 16 to Golden Set Snakebite 17. (For such experimentation, I dont want to waste 17 bucks a string set........)
I can say for me, that the sweetspot definitely got smaller, the racquet was less forgiving, mishits were most definitely felt, and it was definitely lower on power with the tension change. But, when the ball was struck cleanly, it really rocked.
So, I will try this a few more times and see if the strings remain playable longer by starting at the higher tension and go from there. I can probably live with the first couple of hours it playing on the harsh side if it gives alot more quality playing time on the backend of the string's life.
BTJ so far you and I are drawing the EXACT same conclusions.
Here is what I am finding so far after about 5 strings setups.
1. Tension drop is faster initially than other racquets even with good tension mtce polys
2. I am finding that there is a VERY narrow sweet range for this racquet between losing control and being to harsh. So far for me it's that 50-53 range, playing tension not stringing tension. So if you don't mind stringing often then no issue here.
3. The racquet feels greatly balanced for me and solid yet not too broomstick like although its stiff. Although I like stiff racquets so that's personal.
4. I hit with above average spin and honestly don't see the major spin difference. Others may experience more if the are not already producing spin but that factor is null for me so far
5. I'm a decent net player and cannot seem to find my range on volleys yet. I feel the racquet moves well to where I command it but range is off. This may have to do with next factor
6. Ball trajectory is definitely a little higher than normal may be affecting the above issue ?
7. Funny thou deffensive return of serve has been good for me but I believe function of strings here not racquet
After initially falling in love with this stick I am holding a bit of reservation mostly because of the inconsistent play over the hours of a string job. I will sacrifice some performance for consistency because I don't want a racquet feel I have to be chasing the way it performs over a 4-6 hour string job life. I'm gonna do some more testing with other strings and materials and see. I have not tried gut or multi but I am starting to think that a gut or multi in the mid 60s might do well here. Lets see....