77 SMK and IMR8208XBR is a great combo.
I tried 75 SMKs with 8208xbr and my groups were better with 69s, both TMKs and SMKs.
I'm sure it matters what cartridge one is shooting, I hear the 69 TMKs are tack drivers in the 22 Creedmoor.
Honestly, if I didn't have so many cartridges already, I would seriously ponder a 22 Creedmoor build.
I was shooting 5.56 with a Krieger 1:9 barrel, I still have the barrel. If I had a 1:8 barrel, 75/77s would have grouped better. 55 grain FMJs always shot well for me also.
I haven't shot these bullets for 4 or 5 years, so take what I say with a grain of salt. I do have a pretty good memory when it comes to loads, and I usually keep my load data taped to the lid of my ammo boxes. The powders I used were Varget, 8208 xbr and H335. All of them grouped pretty well for me, using 69s, both TMKs and SMKs.
I recently put together a 6.5 Grendel, and the case is huge compared to the 223/5.56 case.
That said, the 5.56 is a fun cartridge to reload, and the 308 uses the same powders. We could probably have a similar conversation discussing 168/175 308 pills, it is yet another horse beaten to a bloody pulp...very similar to 69/75 for the 5.56.