I have never riden fixed in Colorado ( i have mtb'ed and road riden) but I do ride fixed in Michigan. I am thinking you could do fixed/fixed but you would need at least a front and probably a back brake. The mountains out by you are just too big not to run a brake

I get rpm's up in the 180's (172.5mm crank arms and 42x16/15). I do not use a front brake. When I start getting up over 160 rpm's for any extended time, it isn't too much fun. You just have to deal with it.

I have found that crank arm length has a lot of effect for riding fixed on hills. The longer you go the easier it is. If you go too big your knees will scream, too little, you don't get the leverage. I ride 175-180 cranks on my road freewheel bike. On my fixed I have found the 172.5 work for me.

The other effect of longer crank have is that they slow you down on fast descents. From my experience you just can't spin as fast going downhill. I like this because I don't like spinning high rpm's for extended times. Has anyone else noticed this??

I do use a fixed/fixed hub with a quick release. I tried a new DA QR and it was OK but slipped occasionally. What you want is an old school QR. I have one from a 1979 Shimano hub. It is heavy and beefy with big knobs to grab the drop out. It doesn't slip. I don't do a lot of skidding but when I do, it holds. Flippping the cog is easy but usually messy!!