So we're off to do the EBC trek next month. I already own a Canon EOS 40d, I've traveled all over the world, went up Kili and Rainier with it and I love it. However it is a bit too weighty and gets tiring on the shoulders. I expect EBC to be difficult and I don't want such an unnecessary hinderance. On the other hand, I'm doing some research and there aren't any compact size cameras that are jumping out at me and making me think it can match my DSLR. Important features are durability in high altitude/low temperatures, long battery life, hopefully lightweight, etc.

Should I stick with my 40d? If I do, are there any smaller camera bags (somethign like a lowepro) that I can just barely fit in it (I have a 18-35 mm lens on it). Preferably I would want to be able to stash the camera in the bag attached to the hip strap of my trekking bag.

I'm all about dSLRs I like the clik system to keep my camera handy.

http://brad-jackson.info/climbing-with-clik/

I sympathize about the weight and shoulder issues, but I'd definitely stick with the DSLR. I've found that shooting with a compact drives me crazy now that I'm thoroughly accustomed to DSLR responsiveness and controls, and there's no way I'd give up that control on a trip through scenery like Nepal. You also don't want to be just getting familiar with a new camera on a trip like that. If you're willing to keep just the one lens accessible, I expect you can find a nice compact carrier.

There are several small mirrorless systems now with "DSLR" sensors that outperform your 40D. Examples: Fuji X-Pro 1, Fuji X-E1, Sony NEX 5N, Sony NEX 7. They are compact and small, but share APS-C sized sensors with plenty of resolution (16-24 MP, in case of the Fuji without AA-filter, which increases sharpeness) and DR (12 stops+) on-par with the best DSLR systems. No mirror means smaller lenses on smaller cameras. All you really loose is the fast AF of the DSLR. I doubt you need that on an Everest base camp trek.
All of them are also frequently used by professionals. Particularly the Fuji systems (also the lenses) can be recommended.
Look at http://www.dpreview.com, http://www.rangefinderforum.com, http://www.fujifilm.com/products/digital_cameras/x/

Good luck!

I would look at the Rebel T2i or T3i. Both are very light for DLSRs and you can use your 40D lenses.