That's not too bad. I'm 6'2, and my pow stance is 23.5", with my jibbing/rail board set up at 25". I would say find something that's comfortable, but maybe 24" would be a good place to start.
I can't go any wider. I tried going a tiny bit wider and it made my knees hurt when I try to press the board. Also felt weird transitioning from one edge to another.