Can't say I think much of .400 Cor-Bon. It duplicates moderately hot factory 10mm ballistics, but only with the lighter bullets... .400 Cor-Bon factory loads (and even load data!) don't exist for the heavy .400" bullets out there (180-220gr). In the bargain, you get fewer rounds in your gun than 10mm, and for those with double-stack magazines it does not feed well. Aside from their 2 hunting loads, Cor-Bon's 10mm ballistics are intentionally watered down (and chronoed from shorter barrels, BTW) compared to their .400 Cor-Bon counterparts.
If you have a .45 ACP, it is simpler to use .45 Super instead of .400 Cor-Bon to get more power. For the same amount of work & expense it takes to convert to .400 Cor-Bon, you could convert to .40 Super and get much hotter ballistics, or even go all the way to .460 Rowland. If you don't have a .45 ACP to convert, 10mm gives you better ballistics with heavier bullets, is cheaper to reload (think brass availability), has WAY more published load data to work with, and factory ammo is vastly more abundant than it is for .400 Cor-Bon.