I have shot and owned all three at one time or another..The 375 Ruger is the most practical without a doubt, the 9.3x64 is just a complicated .375 H&H or 375 Ruger for all practical purposes and brass can be a real problem from time to time..The 9.3x62 is always a favorite and seems to suit your needs more than the others as you already have a .375 H&H so the first two are repetition of the H&H...
I presently have both a 375 H&H and a 9.3x62, I really like both calibersa as would anyone that has used either on game.
The 9.3x62 has an advantage, for use of a better word, in that it has an 06 type case, it will come within 100 to 150 FPS of the 9l.3x64 and thats close enough, it will take more rounds in the magazine. I can get right at 2500 FPS in the long tube with a 320 gr. Woodleigh. My 375 will get 2550 to 2600 FPS with a 300 gr. Woodleigh, so thats a push in that the 9.3x62 shoots a 20 more grains of bullet but about 50 to 100 FPS slower. I also get 2553 FPS with a 286 gr. Nosler and 2700 plus with a 250 gr. monolithic, Barnes, GS Customs or the Swift bullet in that weight.
My Brno mod. 21 9.3x62 weighs 7.5 pounds naked and recoil is a tad less than all the other calibers you refer to. It has been a great gun to pack around in the Tanzanian heat its light handy and very capable Cape buffalo, Lion, Leopard, gun, and would suit me fine for elephant if I had to use it on one. I would be hard pressed to choose between it and a .375 however.
In as much as my African hunting has slowed down the last few years, I happen to have both my 375 H&H and the 9.3x62 for sale, when one sells then I will definately keep the other in case I have a change of heart and decide on one more venture to Africa, but that will give you an idea of how I feel about your choices.
The 9.3x64 is a fine enough rifle, but just too many problems for what you get, if you just want something different it might suit you fine but IMO its neither fish nor fowl..but again thats just my opine.
