If you've never carried the SBH in the field before I would suggest the lightest possible version. They get heavy. So I definitely would go with the 4 5/8", but with fluted cyl of the 5 1/2".
You might consider two relatively recent issue distributor exclusives:
1. SBH SS with 3 3/4" barrel from Lipsey's:
http://ruger.com/products/newModelSuperBlackhawkStandard/specSheets/0817.html
2. New Vaquero 44 Mag in SS, fluted cyl and 3 3/4" barrel for lightness, and SBH hammer from Talo: http://www.realguns.com/articles/789.htm
http://ruger.com/products/vaqueroStainless/specSheets/10596.html
Personally I don't like the Birdshead grip, therefore I'd swap to the SBH Hunter grip which has more knuckle space behind the trigger guard than the XR3-RED grip frame on the 4 5/8" and 5 1/2" SBHs (which already have more space than the Bisley grips). I prefer it on my field carry gun.
One advantage of the 5 1/2" barrel is you can add the 5" ejector housing for fully ejecting those long Mag cases as also shown here:
You might also consider Ruger's mid frame 44 Spl flat top Blackhawk in SS: