Studies show that narrower bevels provide better edge retention during normal cutting tasks than more obtuse bevels. There is a limit, of course. At some point the edge becomes so thin that it is fragile. With most steels, this won't be an issue unless you go lower than 10 degrees per side or so. Call it 12 dps to be safe. However, if your choice is between 20 and 25, always go with 20. It will stay sharp longer, sharpen easier, and there will still be plenty of steel supporting the apex. If it were my knife, I would bevel it at 17 dps, use it fearlessly and strop it regularly.