I've had both. Sold off the 270 and still have the 9.3x62. Both are great calibers and both have their uses. You can't really compare the 2 side by side since they are so different.

The 270 is great for deer sized game in open country. It shoot fairly flat and the bullets up to 150 grs (the heaviest factory loads) perform well on medium sized game and can be used effectively on larger game with very careful shot placement. It would be hard to find a better deer/pronghorn/sheep round. I sold the one I had because I also owned a 7mm Mag and it outdoes the 270 in every category and is a better choice for elk which at the time was my primary hunting quarry.

The 9.3x62 was developed for German farmers in Africa. As such it fires a fairly heavy bullet at moderate velocity. Most hunting ranges in Africa are reasonable short so you don't need a fast round for distant shooting. Additionally in Africa you never really know what you will come up to. One minute you may be chasing a duiker that weighs 30 lbs and come face to face with a big eland. The 9.3x62 can handle both. The 285/286 gr bullet that is most common will punch through the duiker without opening up so you would have a .366 hole in and a .366 hole out. But that same bullet at the moderate velocity it is loaded to has great penetration and can cleanly take the eland which may weigh 2000 lbs. With solid bullets up to 320 grs the 9.3x62 can efficiently take the big stuff like elephant/rhino/hippo etc... Of course anything I just said about the 9.3x62 also applies to the 375 H&H. But the 375 requires a magnum length action which means the rifle will be heavier and in the old days, more expensive. The 9.3x62 was designed to work in standard Mauser actions and could be made cheaply and sold to the average guy that wanted one rifle for everything.

As stated, I kept the 9.3x62 because I found it so effective. I also have a 375 H&H but I can't remember the last time I shot it. I have used the 9.3x62 exclusively for the last 10 years or so. It works that well. The 270 also works well but there are better rounds that do the same thing. Back in Jack O'Connors day that wasn't true, but it is now. But nothing really improves on the 9.3x62 which is why it has been around since 1905. It's just a shame that more Americans haven't tried it.

You get out of life what you are willing to accept. If you ain't happy, do something about it!