7.62X39 is bit light for deer at a distance. I won't call it anemic, but it functions on the light end of the 30-30's realm.
The 6.8mm Rem SPC is meant to function halfway between the 223 Rem (5.56 Nato) and the 7.62X39.
Don't get me wrong. You will find your share of successful deer hunters toting all three. The 6.8 Rem SPC is a necked down 30 Rem, and the .30 Rem has always been an underrated deer killer.
If it were me, and I was looking for a close-in deer rifle, I would be thinking a 44Mag. The old Ruger 44 Mag semi was an awesome thing in its day. I was sorry to see Ruger take the updated Deerfield off its list.
I used to be a semi-automatic deer hunter. I still keep a couple in inventory. However, I have gone more towards levers and pumps. They are lighter to tote and easier to maintain. I say that, and then look over at the M1 Garand on the rack, ready to go down to deer camp this weekend.
Let me throw some ideas at you:
[ul][*]Remington 7600 in one of its shorter incarnations-- 35 Rem, 308 Win, 300 Savage. This is the animal the Benoits carry. I am very fond of mine.
[*]Marlin 1894 in 44 Mag[*]Browning BAR in 308 Win[*]Remington 1100[/ul]. . wait, what's a shotgun doing in there? Listen, if you are hunting deep brush and are jumping big deer close in, a 12 Gauge Semi with slug provides utter devastation. Just don't try to push it out further than it was meant to go. However, that same warning could be said for the Ruger semis you're thinking. I try to get out at least once a year with mine trying to put the sneak on in the dense cedars.
Just so you can gauge my biases: after 26 years in the woods and a couple dozen deer rifles, my ace #1 general purpose deer killer is a Savage 99 lever in 308 Win downloaded to shoot 300 Savage-esque loads.