Yeah, run it as slow as possible. Mine throws at any higher speeds but will run for 24 hours no problem on lowest setting. You don't need a full vortex, just to keep the yeast from settling to the bottom.
I put some dip-tube o-rings on either side of my stir-bar and it spins much better now. Of course mine has a fulcrum in the center, using a 1.5" stir-bar.