well fellas, I am delighted with the non-S 99. And that is saying something because I have been very successful with various MG and IG Rads recently result wise (MP and OS), had a great hit with the Volkl PB Mid 10 (beautiful but demanding racket) and had a healthy extended interest in the 99S version. However, the non-S really is a fantastic racket and solves the short comings of the 99S for me and my style.
I knew I liked the feel and frame of the Steam 99S but have niggling issues with depth, penetration, leaving sitters if not ripping through every stroke etc. Not so with the 99, every shot was strong and finally I have a stick that is easy rallying and with a truly superb response when you pull the trigger to get the ball through the court fast. My opponent was quite taken aback by the difference in a week. Easy win against a strong player. The 99S has a marginal advantage on backhand slice but not significant.
Veninga, comfort wise it is good simply for this: You must use a poly in the 99S, full bed. IMO, you have no choice. However, with the non-S 99, I played with Wilson Sensation at mid and it felt great. Still tonnes of spin when needed, the 16x18 is already very open but I can't quite believe it myself. A really great racket and finally off Polys at the same time. 99 with Sensation is definitely softer than 99S with Poly but if they had the same strings, I would agree with Jack that the 99S would be slightly softer (or less hard!). However, you cannot put a multi in the 99S.
ps. my only concern is the QC but I have just ordered two additional ones and plan to send all three to a professional stringer I know who can perfectly match them with the one I already own as the target spec. Got to be done.