For one thing, the X-37 Wikipedia page states that a design goal was 3.1 KM/s Delta-V. That's about as official a number as I'm finding online (blah blah Wikipedia source), but there are quite a few people who track these things in the sky. Each orbital inclination or altitude change requires a minimum delta V to execute, and we can observe the results of these maneuvers here on Earth. Online arguments about the X-37 delta-V are inconclusive, we'll leave it at that!