Sinx would be the main killer, easily. They have cloak. Something that doesn't cost a lot of sp. Even with original RO gears, cloak. If you're using original RO gears, means you have WAY less reduction from demi human. There are gears out there for sinx that are pretty damn close to Fdaggers. Give a sinx that, and with cloak, they could easily kill 5 people before dying once. Which is something no other class can do, as easily. Profs and HW will do good, if GTB isn't allowed. But only for so long. And again, sinx with cloak. Or sinx and hide, then grimtooth. Sinx has way too many ways to fight off nearly every class in the game. It's made to kill. This room would only make the sinx better at it.
My two cents.