too late to write up tonight's experience but we won our tournament match comfortably against a good pair and I played good consistent tennis in the first set with the 99S then very aggressive strong tennis with the IG Rad OS in the second (which just plays like a powerful MP version). The main comments from my opponents were that they had more time on my shots in the first set but my shots were much hotter in second.
Still interested in the Steam frame but I think the 99S is going back. Will definitely look at the non-S 99 though and will report back.
ps. a real stand out for me with the 99S is the slice backhand. happens to also be the only main weakness of the Rad OS as it happens.