Horse - it needs x pounds of alfalfa and y gallons of water - Hey, a human being won't drop dead if it goes without food and water for a day or two, a Horse likely would not either. You can run light and fast for a few days, then take a day or two to camp, rest up, get the horse recovered. Hopefully you are only a few days away from your intended destination and the horse will still be salvageable when you get there. Otherwise, you eat the horse, ditch whatever you can't carry to the destination, and trek on. We're talking about survival, right? You don't push it that hard if you don't have to, but if lives are on the line and there is no choice, it's an option.
I'd like to see someone take an 80 lb pack up and down hill and avoid obstacles even on paved surface, and make 35 miles a day - even ONE day. That is LUDICROUS for everyone except the 1% that happen to be current enlisted Green Berets or rabid hikers. I took a hike thru Yosemite with some buddies of mine a couple years ago... we are average representatives of our age group (35 to 45), reasonably fit (read: not 400 lbs or in a wheel chair and can mow the lawn without getting winded). It took us 3 days to make 23 miles from trail head to trail head. Previous hiking/camping experience with a full pack (NOTE: no firearms or ammo!) leads me to believe this is par for the course walking in varied terrain, about 7 miles per day. I laugh out loud when someone mentions taking 1000 round of shotgun ammo with them. Weigh it sometime. Then put it in a pack on your back and walk a couple miles. Then add in all the other gear like a tent and water filter and any other basic gear you'd need to make it 20 miles from home on foot.
Now I'll answer the question: if solo, I would take .357 revolver and Timberwolf pump carbine. If in a group, semi-auto handgun and light semi-auto carbine (group standard on pistols and carbines preferably). The reason for the .357 combo is to cover the contingency of having one of the guns lost or disabled - all the ammo is still usable, you haven't wasted energy hauling ammo you now have to dump because the gun that used it, doesn't work anymore.
People sitting in front of an internet keyboard tend to forget that ammo is mostly LEAD and is heavy. I've always been disappointed that video games seemingly let you carry unlimited weapons and ammo without assessing you a weight/strength/speed penalty. That's just not realistic.