DF,
My personal opinion is that those are the two bullets for the .375H&H that should be considered. Nothing wrong with the 300gr, I am just a big fan of the extra velocity with a flatter trajectory. I have not noticed a difference in killing ability between the two.
Lately, most of the guys pitched up here with the 250's , but just for plains game, and they were hammering them across the valleys.
As I mentioned before, I would not hesitate for a second to use those 250gr on Cape Buff. We shoot 200gr out of mine for the Buffalo, and they really put a beating on the buff.
That is without a doubt where I have seen a difference. The 200's are doing 3200fps, and there is a visual trauma upon impact, which I can only assume comes from the high velocity.
I think that 250 TSX/TTSX is as deadly as what you are going to get from the .375 and you can use it on anything.