For a low cut on the vocals, I'd try going as high as you can get away with. A lot of things I cut around 50hz, but you might want to try even as high as 100hz, 150hz, or even higher. The more low end you can get out of things that dont need it (everything but kick drum and bass usually) the better.
For blues type stuff it might sound just fine with even a relatively high high-pass frequency. stand rumble's probably around 50-100hz, but there could be other low end stuff that will muddy up the mix, and isn't necessary to the tone of the vocals.