I can see him winning against Plagueis because he has more powerful TK and Lightning, plus he has dark transfer and is just more trained for using the force in a combative setting.
I don't think he'll be pulling decisive victories over anyone else, though.
Valkorion is more powerful in the force, both combatively and not. Krayt's a better lightsaber duelist, but Valk doesn't really deal with that. It would be a force-based fight, and Valk would win.
Knightfall Vader is more powerful in the Force and with lightsabers, though much more stupid, so Krayt might just win relying on Anakin's stupidity.
With Sidious, he could put up one hell of a fight, and defenitely leave the emperor in critical condition, but I don't think he could quite win.
He would lose to GM Luke. He could still put up a fight, but only the kind he did when fightning Kenobi on Tatooine. He would lose 10/10.
This is kind of a loss for Krayt, but not at all a loss for ILS. That respect thread defenitely pushed up hype for Krayt. He doesn't win against most of these guys, but just how much of a fight he's capable of putting on alone is ridiculously impressive.