I had Terry build me one after I read that article a few years ago. Great rifle, but IMHO the improvement is not worth the hassle of fireforming. I would do it again in a straight .260 or 6.5x47 Lapua.
Plain and simple- you will gain about 75-100 fps over the standard 260, and have a PITA time working over brass. And Terry now runs a standard 260, if that tells you anything. If you want more than a 260, get a 6.5x284 case.
Not worth the extra cost of dies. Didn't mind the fireforming once I got the dies set up. I had a 7-08 AI which was more accuate at velocities obtainable as non-improved. Very dissapointing but dang if the round didn't look sexy.