I'm heading out to Colorado from the East coast at the end of August and will be doing a 4 day/3 night backpacking loop with my buddy. Unfortunately can't do the Durango/Silverton trip as we won't have time to deal with the train. I'm currently researching the three loops below. I'm going to eventually do the four pass loop with my wife, so I'd like to save that one.

A few questions:

I'm in excellent shape (run 8 miles/day, usually backpack ~15 miles/day and I've done up to 35 in a day), but I'm used to hiking out on the East coast. Will I be able to cover the same mileage out west (10-14 miles/day)? For being in such great shape my body does not deal well with altitude, which is a concern. I'll be out in Colorado for 3 days prior to the trip at 7,000', which I hope helps, but the elevation usually catches up with me on day 5 for some reason.

I'm leaning heavily toward the Holy Cross wilderness loop. However, that loop is only about 28 miles. I was looking at my Nat Geo map and see that I can add a loop to the top of Vail via Elk National Recreation Trail->Gran Traverse trail->Game Creek trail. However, it'll bring us back into Minturn (a bummer to be back in civilization, I prefer to be in the wilderness the entire time) and then we'll head out in the Holy Cross Wilderness. Is it even worth adding this or is it just adding miles for the sake of it? Any other options to add about 14 miles to the Holy Cross loop?

Any other suggestions for loops besides the ones below? Looking for epic mountain scenery, high alpine lakes, trout fishing, etc.

Maroon Bells/Snowmass Wilderness (Not the popular four pass loop, this is west and shares only about 5 miles of trail)
Lost Creek Loop
Holy Cross Wilderness loop