Hmmmm… Firstly, this advice is worth exactly what you paid for it.
In my experience shooting wily and nervous whitetails that have been dog hunted for 400 years (the south 🙁 ), your odds go way up if your bow shoots at least 160 fps.
If you had some kind of super heavy extreme FOC arrow that would maybe compensate for a bad hit, then maybe. But the arrow you specify isn’t really all that heavy. It doesn’t meet the Ashby 650 grain threshold for bone busting.
It also really depends on what your goal is. If you are willing to wait all season for a 10 yd or less shot and can go without meat otherwise, then ok. If you need to feed the family, then I think you might need a faster setup.
I own a 50lb Northern Mist longbow too. But I could never get the performance out of it to justify using it. I imagine in much higher weights, 70lbs plus, the bow does fine. But in lower weights, it’s just too slow.
I was shooting a 600 grain arrow out of my Northern Mist and getting in the mid 130’s. This should not be taken as a disparaging comment about the bow. It has many great features. Speed is just not one of them.
What I did learn from the Northern Mist bow, and maybe what you have learned too, is that you like the american semi long bow. There are many other makers out there.
Before you buy, you can always press them for real performance data. Ask them at what speed their 50b bow will shoot a 650 grain arrow. As I said before, my threshold is 160 fps. In fact, I will sacrifice some arrow weight to get that speed when shooting deer.
My 48lb home made american semi long bow drawn to 28 inches, will cast a 620 grain carbon arrow 163 fps. Four deer are in the freezer this year, taken with this bow.
You asked a good question. I hope I have answered it in kind. There are those that will claim speed is irrelevent. I am not in that camp.