The gibbs has more case capacity than the .30-06 AI. The way I understand it, the Gibbs is more improved than the AI. The case is blown out with a steeper shoulder and shorter neck. You're looking at just under 3000 fps with a 180 gr bullet. It's about par with the H&H and the wsm and about 200 fps over .30-06 spg. I have spoken to several gibbs owners and they all rave about their cartidge. It's not a "magnum" and there is no belt. The only downside is forming brass and expensive dies. Don't get me wrong, the .300 H&H is a good cartridge and I would like to own one some day too.
There are tons of used .30-06 rifles in all price ranges, any one could be chambered to .30 gibbs without changing barrels, and tons of brass, cheap brass. I guess it comes down to what ever turns you on. My problem is that most of them turn me on.