If you think our moral concern should follow intelligence then it follows that chimps and the mentally handicapped are not morally equal to humans of normal intelligence. Depending how much differing intelligence results in differing moral consideration this could justify chimp and mentally handicapped testing.

But while some level of intelligence does seem to be necessary for an animal to suffer in a way we find morally compelling it does not follow that abusing the slightly less intelligent is at all justified. It is not at all obvious that the mentally handicapped or chimpanzees suffer less than humans of normal intelligence. Nor is it obvious mentally handicapped humans and chimpanzees don't differ in this regard. But intelligence is almost certainly not the same thing as moral value. There are possibly entities that are very intelligent but for which we would have little moral regard.