I have 120gr Sierra PH, 140gr Sierra GK, 120gr NBT, 140gr NBT and 140gr NPT.
Aidans 7-08 shoots the 120Ph well, Konnors gun shoots the 120NBT. Both are running 4350 at this time. I cannot remember the exact charges. Whitetail loads.
I'm planning to run the 140NBT or the 140PT in my M70
If I cannot locate the BG I will probably go with the 4350 as well.
H4350 is the best powder for your 140s, if your 4350 is H and not IMR stay with it.
Here in Az may be different but our temperature swings can be extreme, add in driving an hour can take you from desert floor to high elevation and temp differences.
I tested BG with the 120s, both NBT and TXS, NBT shot MOA at 200 off the tailgate and bags in the desert, 3160ish from a Tikka. At the same time I tried H4895 max load, 3080, 1 inch at 200.
The big difference was the SD was 3 for H4895 and 22 for BG, also my buddy standing to the side commented that the BG was really harsh sounding compared, I could feel some difference in recoil.
This is what my wife uses and my loaner for other family, last year my brother shot a cow elk 1 weekend and the next week my wife shot her muley buck. It may be 100 degrees in the desert deer hunt or 4 degrees on an elk hunt. The 120NBT kills both easily including shoulder shots, this is multiple years and animals experience.
The SD, slight accuracy advantage, milder load, and temp insensitivity was worth the 80fps. BG at least here in AZ with the temps was a bit jumpy.
I traded the BG and TSXs a few months ago for some primers so it was a win/win.
H4895 is impossible to find also, just don't get locked on BG over the extreme powders... H4350 is the best overall powder for the 140s.