Yeh, I think you've mentioned those sort of benchmarks before.
Unless I order specific components from the USA, which would be fairly cost prohibitive, getting an arrow that heavy is going to be almost impossible.
I don't know where I'll land with anything yet, but I have some friends who have killed dozens of buffalo now, using fairly heavy recurves and arrows around 550gn. They, like you, have the luxury of longer draw lengths, which I don't have. One of them used an osage selfbow around 55# with a wooden arrow and a broadhead he knapped himself to kill a buffalo cow last year - very cool!
I have some 250 spine arrows available that are 4mm, so the components don't make me feel as good as 5mm arrows, but they're heavy enough that I could get an arrow over 650gn without too much hassle. If I have a trad bow I can tune those arrows with, that's likely where I'll start. They're too stiff off my Widow, I think.
In any case, I was just bumping the thread to give a bit more perspective on the Uukha limbs. I really enjoyed the ones I shot on the weekend.