I'm not sure I'd look at Kirk's comments as racist. In such a trying, emotional situation he (or anyone) isn't about to parse their words carefully, choosing the least offensive term. Especially in Kirk's case, as the situation didn't (in movie reality) take place with a huge audience of listeners. Remember, in a movie we aren't "really" there.
Not to mention that Klingons aren't a race, they are a species.
Come on, if someone put "black" or "white" in front of "bastard," there would be no argument that it's about race. Of course it's about race. The rest is just the same, at best, rationalization a closet racist makes to try to deny that he or she is racist when called out on having said it. It's in trying situations our true selves come out, and the awful or hurtful things we want to keep hidden often get revealed.
I'd use "race" since Gorkon's daughter says more or less that particular concept in the film vis a vis the humans.