If you cant find an H5 or H6, you could try one or two of these:
http://www.robotpower.com/products/scorpion_XL_info.htmlhttp://www.robotpower.com/products/s...n_XL_info.html

Some pics of the setup we used on Killerhurtz:
http://news.killerhurtz.co.uk/newservos/http://news.killerhurtz.co.uk/newservos/
http://news.killerhurtz.co.uk/newwheels/fitted.jpghttp://news.killerhurtz.co.uk/newwheels/fitted.jpg