If you must kill that buff, here's how. You know he wants the base, right? Forget about chasing him, that is his game. Take the time to get above it, at least 2K. Yes, that's tough at that alt, but you need to have some alt in the bank. Position yourself so that he must pass under you to get back to his target. If you time it right you will catch him on the bomb run, so you will get a few seconds to split-S and take something vital away. Even striking an engine will help, forcing him to drop some alt and/or slow down. This has to be done carefully, but if you are lucky you either kill him outright or wound him enough to lower him to attainable alts. Once the fight is below 30K you are in a much better position to fight as you would like.
Be warned, a good buff pilot will eat you alive at 35K+.