.44-.46 would be the range. Depends on 4-stroke vs 2-stroke and your weight/riding style. The two-strokes use lower rates. You can use 1 stock spring and 1 stiffer spring to get in-between rates.
A total rate of .42-.44 should be about what you need. If you have any friends that have 4-strokes, they came with .42 stock. That would be a cheap test.