Thanks fiveO - The photos illustrate two very different types of action and make for good talking points - the first photo requires a good short shutter/lag and if that's the type of action the OP is after that's great. The second photo is a more challenging task - and it's a good shot for the OP to think about if that's the type of framing and IQ they're after.
Or is their expectation to get action IQ that matches still image IQ:
Or if they are expecting to shoot a bit tighter.
Note: I personally am not a fan of dog racing and I don't want to derail the discussion but I wanted to show some photos for comparison - just to be sure the OP has expectations that match the equipment being considered