First of all, you need to tell us what you mean by "long range." The nature of the 375 H&H Magnum is that its velocity is quite adequate but not sizzling. If by long range you mean 200 yards, then it's quite up to the job. If you mean 500 yards, then you will have quite a challenge in knowing the exact range and knowing the trajectory of your loads very well.
Also, why do you want "fast burning powders?" In the 375 H&H Magnum, a fast burning powder will probably top you out on the pressure before you get the velocity you want. In my opinion, RL-15 is about the best 375 H&H Magnum powder out there.