Without specific data, the answer would be a useless guess. The answer requires bullet weight, ballistic coefficeint, velocity, etc...
There are many online ballistics calculators that you can download to determine this for yourself. Hornaday has a basic version, Applied Ballistics has a more advanced program. To name a few. Everyone has their favorite.
I would have to say yes it will affect your ballistics. It doesn't matter what the bullet weight or caliber. The bottom line is the air is thinner and therefore less resistance. Obviously different calibers/bullets will be affected different amounts. Ask your guide, they would probably be able to help you out the best.
I know from watch golf on TV that when they play in Denver, the ball flies farther.
I would a bullet would drop less, just thought maybe someone on here would have had the experience and would know. Am going to ask my guide. I hunted at 5,000 this year and he said not to worry about it.
You'll probably want to shoot your rifle when you arrive to make sure it;s still on zero.
I can tell you that I haven't seen any effect on my point of impact for my archery gear. I shoot frequently at camp which is about 8200 ft. I get the same point of impact at all distances out to 0-50yds that I have here at home.
All the high country hunts I ever did, the guide made you shoot when you arrived. I have never had to change zero from Pa. to Our Western states or Alaska. Biggest thing to remember is, you may get a shot of extreme angle, up or down, that you don't normally encounter in PA. A good guide will advise you to hold slightly lower on a hard angle shot.
I agree with Joe, your zero may change but it would only be slightly and most of that may come from a change in temperature and the changes that would cause in velocity.. He's also right about angles..take a trip to a strip cut somewhere and practice a few shots up and down a high wall if you can, you see quickly how much difference there is. Also no one mentioned getting your rifle in shape..get it degreased,put some cold temperature lubricants in the action.. run lots of lighter fluid through the trigger assembly to get all the junk out and practice shooting a cold dirty barrel...chances are they'll make you fire a shot to check your scope and you'll be hunting from that point on with some dirt and a cold barrel..also practice in cold temperatures it does matter to those fingers. good luck
I hunted New Mexico at around 9500ft. I missed the first shot at my Mule Deer at 300 yds. because I aimed to high thinking there would be alot of drop. After I missed my guide said:"This aint Pennsytucky son this is New Mexico and your at 9500ft. Aim dead on and you wont miss" My next shot at the same deer was at 382 yrds. and I hit the deer exactly where I had aimed.
Thinner air means less bullet drag, which means straighter flite is what I was told.
I shot a 300 win mag and was sighted in at dead on at 200 yrds
Ive been hunting in Co. last 4 years and my zero was the same as back here. However as mentioned your going to shoot flatter at higher altitude. You need to down load a ballistic calculator and you can figure out your droppage. You will need to know your bullet, bc, elevation and vel. than you can run the numbers maybe making yourself a drop chart. I actually last fall just purchased the new gunworks G-7 range finder calculator. One i shoot my range it comes back with the correct moa to dial in. It actually calculates the elevation, temp., baro pressure,angle and gives me the reading.
Ted I hope you don't have any bad weather, but if you do, one of the neatest things at that elevation or higher is to watch weather ( Rain, snow, lightning) occur BELOW you. Its something you never forget.