Gents:
It's great to read all these opinions of the two greatest big-game cartridges of all time. It goes to show the timelessness of these two great rounds. While I have never owned a full nitro .577 (I've shot several) I do have some experience with the .600 and I thought I'd throw in my two cents.

Recoil. When Bill Feldstein was developing the .700 H&H in the late 1980s it was determined that the most recoil an experienced shooter could tolerate was that of a .600 NE. To make the .700 have approximately the same felt recoil of the .600 the weight of the rifle should be 19 pounds. My theory (unsubstantiated) is that 110 years ago when the .600 was being developed (1899) it was determined the recoil of the .577 was about as much as a shooter could tolerate. So, to make the .600's felt recoil the same as the already popular .577 the weight of the rifles was to be 15 1/2 to 16 pounds. This makes sense to me, anyway. If one calculates the recoil of both cartridges with full house loads, the recoil figures are about the same if the rifles weigh 13 and 16 pounds. With the rifles in this weight category, one will not kick more than the other as long as the stocks fit the shooter the same.

Penetration. Everyone, beginning with John Taylor, has noted the .577 penetrates deeper than the .600 as most of the vintage bullets of the .600 were rather blunt. Some have asked why Kynoch and Eley didn't make the .600 bullet more pointed such as the .577s bullets. I have a theory about this, too (also unsubstantiated). There is no doubt the English make the finest guns in the world and they also invented big game hunting. They knew what they were doing in all aspects of firearms manufacture. I feel they developed the .600's blunt-nose bullet to avoid over penetration--if the bullet were more pointed it would pass completely through the elephant. I know the debate will go on forever about two blood holes or the bullet expanding all of its energy within the animal and it was debated 110 years ago.

Which is better. Neither or both--your choice. Both will kill anything on the planet but both will just wound with poor bullet placement. In my personal experience on buffalo with a .600 is this: when hit in the shoulder there is no difference that the critter being hit with a .375. It does not bowl the buffalo over. Most of the old hunters used these big rifles as backup and rarely used them as a primary rifles (Sutherland is one exception, Anderson is another). Today they are needed even less but they are fun. Owning an original .600 is the highlight of my hunting and collecting.

Cheers, all
Cal