I have used IMR for 30 years for 155, 168 and more recently 175. I did a class with some hot 8208 175 loads which is a faster powder and consistently hit at 1k, but I won't do that again. Varget seems to be a favorite as well as 4064. Of course as someone pointed out 4895 is old school as is 4064, but as long as you watch the pressure signs and don't try to shoot on a 105 degree day after leaving your max loads in the sun you should be fine. I think H is considered one of the extreme powders so in theory it should be better, but maybe not as good as the Varget. If you are loading for a semi, you don't want to go max load, unless you want to abuse your gun.