Nothing wrong with the Sierra GameKing 150gr BTSP.
Speer...I've never loaded any of their .277 bullets so I can't give a review on em.
Nosler Ballistic Tip...All weights of the .277s are very destructive on deer meat (Yeah...I know hit em in the vitals instead.
) And the jacket & core do tend to separate. We've wound up picking lots of bullet jacket shards out of the sausage from a friend's Ballistic Tip loads.
Nosler Partition would be a better choice for deer in my opinion over the Ballistic Tip. They're too spendy for my wallet though for just deer, but if I was working up an elk/moose load it would be either Partitions or Barnes TSX/TTSX
Is there a particular reason you're sticking with 150gr or are you open to other weights?
I've been loading 140s for dad's Rem700 for the past few years but before that, it was 130s. 140gr seems to be that middle-ground compromise between the old standard 130 & 150 weights...and it seems to work out pretty well.
Dad's rifle likes the cheap Winchester 130gr PP but when that was hard to get a few years ago I switched to the 130gr Sierra ProHunter.
I've got a bunch of Midway blemished 140gr (Hornady SST) boat-tails that it shoots rather well and I've tried the Sierra GameKing 140gr SPBT but that rifle seems to prefer flat-base bullets...at least with the loads I've tried.