Without getting into too many details about testing standards, the SA ratings were developed to be more appropriate for motorsport use.
This includes differences between standards regarding eyeport size, conditioning, impact energies, test anvil selection and test criteria in addition to the fire resistance mentioned earlier.
Although the helmets look alike, and there is some overlap in testing: buy the one that 1) is applicable for your purpose, 2) fits and 3) suits your budget.
For what it's worth, I'd use a full face helmet for any sort of track use.