When you are bugging out, you don't want to stand out. You should stay away from heavily traveled roadways, stay away from urbanized areas, and travel light. I would suggest keeping your pack under 35 pounds. That's the Army's weight for 12 mile road marches. Its not an easy task to carry more...
I would buy the best one you could afford. Do some research on what some people are saying about Military rifle testing. The M24 (Remington 700) rifle is great for precision, but slow on multiple engagements and limited to an internal 5 round magazine (M24A1) or 10 round detachable magazine...
One aspect you haven't considered was barrier penetration. While the maximum effective range on a point target of a fine AR rifle is slightly higher than 600 meters, what if you had to fire into a barrier at say 300 yards? Glass, plywood, brick, etc.? The question then becomes one of ballistic...
I feel you should buy similar weapons. Then I would buy a few extra parts. That way you have interchangeability with magazines, parts, and ammo.
Mosins are nice, however, in a sustained SHTF or TEOTWAWKI situation, how common will 7.62x54R be? 5.56, 7.62x39, 12ga, and 9mm are very common. If...
If the SHTF you want something that is common, .338 Lupau is nice but who has a large amount of ammo? I would stick with NATO or Eastern Block rounds. When I was in Iraq, I had an AK for back up, the reason being, if I ever ran dry of 5.56mm, the more of them I shot the more ammo I could find...