Because there is no specifics/information that is canon on the droid. Could Revan make another assassin droid? Yes, would it be allowed for this? No, reason being...its pretty much a blank chassis and you'd be able to throw in whatever to make sure the assassin droid is the best thing ever.
Without actual canon information, its just not gonna fly here.
Just use similar specifications as HK-47 or an HK-50...
In any event, if Revan can force Xizor into having to play this as a military campaign, Revan will win.
If Xizor can force this into an underworld style situation, he has the advantage.