Chaotics are level 80, Drygores are level 90. To my knowledge, there isn't a level 85 weapon. Anyway, (assuming you're talking melee) Off-hand Chaotic long and rapier both have the same stats, just different styles (slash, stab). You'll have to consider what you'll be killing most of the time and check their weaknesses. If you're going to be doing slayer, which gives you random monsters, then it really doesn't matter because if a monsters weakness isn't either of the weapons attack styles (say, weakness to water spells) then the damage will be the same for both.
I'm not sure if this actually works, but since there's no bonuses to having matching main and off hand weapons, you could try getting the opposite of what the main hand is. So if you have an off hand CR and main hand CLS and get something with a weakness to stab, then there could be some bonus damage there. I'm not 100% this would work, but I imagine it would.