If you are planning to sleep at elevation, in Colorado, in the summer, then you need to prepare for temperatures much colder than 50°F. OM's advice is good. If you tend to sleep cold then you should be looking at a 20°F rate bag. If you tend to sleep warm you should be looking at a 30°F bag. ... and that is the rating from a high quality manufacturer. Certainly not somebody like Aegis. Some people do quite well with an Aegismax bag, but you have to know what you are getting into. The temperature rating does not mean anything. Look at how much down they are putting in the bag and compare it to the amount of similar quality down for a comparison of what it should be rated at. The other thing about Aegismax I have heard is that they are not designed for very big people. If you are more than like 5'8" and a 160 lbs you might find it a bit of a squeeze.

Have you considered a quilt? The last two sleeping bags I have bought were quilts from Enlightened Equipment. I've been very happy with the purchases. Lightweight and at a great price. The insulation underneath you in a sleeping bag gets compressed and doesn't keep you warm, so just get rid of it!