The problem is that even with the faster shutter speeds, I still can't capture the perpetually moving target AKA Hazel with complete clarity. Even at night when she was winding down, she still twitched and moved a bit so none of these pics are completely "nailed" in the eye area like they should be.
I'm discovering that it makes a big difference whether or not a lens has IS (image stabilizer). My original lens, an 18-55mm zoom, had it. My new lens does not.
I could hand-hold my old lens at a shutter speed of 80 (or even much slower if I braced against something) and still get crisp shots. I can't even do that at 150 with my new lens. Which means I have to use a tripod a lot more, which means I lose flexibility of shot angle - or it at least takes me a lot more time to get the tripod all changed around to shoot from a different angle!