I would think you could use up to ISO 3200 without any issues (maybe even up to ISO 6400, but after that, I find the decrease in DR range can impact higher contrast shots), so you have room to spare with your current set up. If you need faster glass, I would think you would be looking at 85 f/1.8, 100 f/2 or 135 f/2 to give you two stops of improvement, depending on which focal length would best suit your needs. But, as I said, your current set up seems to be working. I agree with decreasing the angle to get on the same level of the skaters.