What we saw of the Voth leads me to belive they are a very powerful race.
Personal Cloaking Devices
City Ships That can swallow an intrepid class whole and disable it effortlessly.
I don't know how many ships the Voth have though, I would assume that in a battle the Borg wouldjust outlast them due to superior numbers
1 on 1 I think a Voth ship could take out a cube though