Ah, too bad this ability is both 1/day and completely useless. It has to be entirely disregarded to assess the monster's power, basically. Rogue seems a good choice: going Maiming Strike allows you to double up on Cha damage up to the point where it's a OHKO on a lot of monsters. But the utter lack of anything useful brought forth by the racial HDs makes me think that 9 or 10 RHDs is quite a lot, already. I'd go 7: this way you can nab 2 Rogue special abilities before level 20.