It's absolutely true.
Vette will attest that the Sith Warrior is a god in the bedroom. Kira Carsen informs us that she has been sorely disappointed by the Jedi Knight in comparison.
Oh, do you not mean that kind of performance?
That's not really a reliable source cause she has a shock collar. I'm sure if you had a lightsaber at Kira's throat and asked again, the answer would be quite different.