I personally havn't hunted the area you're talking about.

I have hunted Id. in the Salmon's. Beautiful, rugged, unforgiving, and on and on. We hiked in and hunted high for the first couple days, taking a beautiful buck. Then the weather changed in a matter of an hour and we got dumped on. The wind knocked a tree down through camp ( over my tent) and the snow had blown into everything. We packed out, got dried out and then hunted some low ground the last day.

I used a 7mm RM with Sierra Gamekings, and my buddy used a .270 Win with 150gr Ballistic tips. I was happy with the performance of my choice on a three point that was a easy 125yds or more. Full penetration with mush in the chest cavity. The .270 w/ BT's wasn't what I expected. Poor shot placement may have had some of the blame but it was a huge buck. After seeing the end result I am careful about recommending BT's over much of anything ( except Hot Cores) and would quickly recommend the interbonds in the .280, and recommend at least a 165gr in the '06. Obviously shot placment is the most important factor. The BT's work like lightning when the shot is exactly where it's supposed to be, but not everyone can be as good in the field as when they are practicing.

Plan on the weather being everything from mild and sunny to stormin' and cold all in the same day. I myself have gotten a top quality sleeping bag, better rain gear, and Danner boots as a direct result of my experience on our trip. I literally broke my Rocky boot sole in half, My Mil surplus mummy bag wasn't enough when the storm hit and was hard to dry out. MRE's are heavy, hard to warm up, and have a lot of packageing to haul out. ( Taste the same now as when I was in the service 12+ years ago, BAD!) My tent could be better for the extreme weather too but I havn't replaced it yet. It all really depends on how you are going to hunt, how you're going to camp ( or not) as to what you really need for equipment, clothes ect. The rifles and bullet choices are fun do discuss but for deer aren't really critical either.

Snider, I can't add too much to the good advice given by Nate. As he said, your rifles are just fine for any Mule deer in North America. My favorite all around deer/antelope rifle is a .280 Rem. using the 139 grs. Hornady Interlock. That 139 grs. Interbond of your's will work just fine.

As said, especially in mid-October, be prepared for weather changes. As you've hunted in Wyoming, you've probably already seen rapid changes in weather, so have the proper clothing and equipment.

I've not hunted Island Park, but have hunted about 50 miles south of there. Great Mule deer and elk country, for me and my partners. You'll have a chance to see some moose up there, also.

Good luck.

L.W.

thanks big nate for the reply.

Although its been a few years, I had my best luck in the Soda Springs area south. I suspect you will have less pressure in that part of the country, especially if you get away from the road.
Good Luck