Well I did a little research and spoke to people and the opinion is that it's best to stick with the standard ratio. Given the weight of the car (3850lb), the size of the tyre (10.5) and the HP (850 ish). The reason I asked is after I'd stripped my g'box down I found the front planetary and annulus damaged. Commom problem, so we've upgraded to a 5 pinion all steel and rollerised annulus.
Just thought I'd pass it on.
Cheers.
Tig.