I can't speak for hard numbers but I have a couple low end might slayers that I use that still hit the specific victim harder than a normal vanq does. Just my experience though. I'm sure we got a nerd or 2 here that probably has an excel spreadsheet on it.
I have no spreadsheet but Slayer = Double Damage. It is known. Magic Modifiers are 1/3/5/7/9 for Ruin/Might/Force/Power/Vanq. I'm not sure if the magic modifier is applied prior to the 2x damage of the slayer attribute, but in any regard, if the weapon does more than 9 damage, it will definitely hit harder than a vanq as a base-level Slayer weapon only. For example, the Large Battle Axe does 6-38 damage. As a Slayer, it would be hitting for 12-76, whereas a vanq of the same weapon would hit for 15-47...I think. TL: DR = Even a bottom end Slayer is better than any other modifier could be. The weapon in question: http://www.uorenaissance.com/info/?page=info&id=2022 Would do 6-56dmg +1 (so potentially 8-58) damage and with the speed of the kryss...that'd be pretty sweet. Sadly you'll be repairing it constantly as well to keep the damage up.
I have a fencer that is yet to be finished off so i may as well do it whacking on mentals. I'll start it off with 10k.
Yes yes, I have "an" excel spreadsheet with this stuff :/ (Actually have not had a chance to test slayers yet, because I have no idea how to whip them up on Test, besides bugging Chris or Ezekiel to create them for me).