Martian:
If you're going to be making one that can climb stairs, you'll want metal ones like Kenny Kong makes. The grey composite stock ones will not hold up to extreme manuevering, as the area where the link-pins are is not fully sealed. Kenny fixed this when he cast his, and they are very good, and provide a lot of traction.
Willy Loewer has a video of one of his modified Kitties climbing at least 45 degree slopes: http://www.customrcmodels.com/id455.htm (scan down until you see the King kitty on the ramps...)
You can get Kenny's tracks through: www.BackyardArmor.com or direct off Kenny (PM or email me for his addy)
Track total run length: 870mm
Track link width: 51mm (combat tracks, transport tracks are narrower)
Hope that helps you out.