canoe-
Here is what is listed in the article. I was off on the energy listed in this article as being 10,000 ft lbs. I haven't read it for quite a while and was going off memory. (not a good idea apparently) The 10,000 ft lb figure came from an article by Ross Seyfried on the 585 Nyati that he designed, and wrote up in the G&A, December 1991 issue.

600 grian Barnes soft nose
152 grains of IMR 4831
instrumental velocity=2578 fps.
ft lbs of energy=7500

700 grain Barnes soft nose
132 grains of IMR 4831
instrumental velocity=2260 fps
ft lbs of energy=8400

The above loads are listed on page 100 of the February issue, 1989 Guns and Ammo. The standard factory loading for the Gibbs was a 525 grain bullet at 2300 fps.