I would imagine something like 2d10 (or possibly 2d12, depending on how devastating you want to model it), with an 80 foot range increment. One question I'd have is: how much energy is transferred to the target with a .600 H&H verus say a Barret light Fifty? The .50 round is a smaller profile round, but more aerodynamic.I've never seen an actual .600 round, but I've imagined them to be basically hopped-up shotgun slugs.
EDIT - more info on the .600:
http://members.ozemail.com.au/~mickay/nitro.htm
Most interesting points:
The .460 weatherby magnum now holds the record for "most energy per round" at 8,245 foot pounds. The .600 nitro clocked in at a, ahem, respectable 7,591 fp.
I am mistaken on the "shotgun slug" idea - it's a true cartridge, and a 900 grain one at that. The rifle weighs around 16 pounds.
Bullet Weight; 900 grains
Muzzle Velocity; 1950 fps, Energy; 7591 ft/lbs
@50 yards
Velocity; 1794 fps, Energy; 6427 ft/lbs, Time of Flt; .08 sec
@100 yards
Velocity; 1646 fps, Energy; 5413 ft/lbs, Time of Flt; .17 sec
Anybody want to use Wulf Ratbane's Grim Tales rules to calculate expected damage off these figures?

I'm afraid my copy is at home.