Which lens for job - 17-55 2.8 or 50mm 1.8?

Ive been shooting portraits and action shots of the pros at my local tennis club. Its pretty well- lit, but indoors in a bubble.

In the past I've used the 50mm 1.8, as it was the only fast lens I had. It, together with my skills and experience at this, had good results, though the action shots were always tricky and I had to shoot at 1/500th to really freeze the ball and player, needing high ISO of 1600. I reduced noise later in LR.

I just purchased the 17-55 2.8, (love it!) and have another shoot on Friday with two pros. I'm wonderimg if the newer lens will do a better job for portraits and/or action shots.. I wont really have time to experiment much, maybe take a few test shots. I'm wondering if IS on 17-55 will make up for less speed on portraits. I don't think IS will help much on action shots. Im also wondering if 17-55 2.8 will generally give me sharper, cleaner shots and more contrast than nifty fifty In this situation

Anyone have any opinions or experience that is relevant? Thanks in advance!

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Sam K., NYC