well what sort of resolutions do you want to cater for?

This is the the problem with horizontal over vertical, people more naturally look up and down than side to side, so you may well get the same amount on a large monitor with horizontal and vertical scrolling. But horizontal just feels odd, its hard to describe and probably easier to experience. =/

could always try making it bigger vertically? you run the risk of alienating those with really small screens then mind.