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If the IQ, AF speed or anything else about 70-200 2.8 IS mkII disappoints you, you will likely have a long wait for something better to come along.
You said you shoot indoors and if the 70-200 range suits your needs get the 2.8 IS.
The AF is fast enough for the racing, but the IS may not be needed and the f:4 will likely meets your needs (but the 2.8 can be used to increase your SS). The only question might be is where to shoot from. After all, it is only 200mm at the long end so you may need to find the right best location to get the shots you want (e.g. coming around a turn). Using a TC will slow the AF (which is blazingly fast), but I havenít tried mine with a TC yet to determine how much.
I have also heard very good things about the 70-300 L (I donít have it), comparing it to the new 70-200. Some have said the IQ and AF speed comes close if not rivals the 70-200. While it provides more reach you may want for racing, it is f:4-5.6 and may not suit your needs for lower light capability. Still, it is a little cheaper than the 70-200 2.8 IS mkII.
Getting the best, even if it offers more than you need, is not wrong. What would be wrong is getting a lens only to find out it comes up short and you purchased the wrong one.
I chose to go for the 70-200 2.8 IS mkII for my situation and needs, but it will be your decision and you will need to live with. Good luck with it.