I'm still working on my demo reel but from my research, I think you should make different demo reels to target specific positions that they need...like show tons of clips of different characters doing different things with different emotion for character animation job. Or if it's modelling, show lots of it turntable style. If it's everythinig, then show everything. I think companies only look at things that they need at the moment, only, so the rest of your content may be viewed in fast forward.
But of course, I've read somewhere someone got hired with a clip of only several seconds long...just to get all our hopes up.
"Whatever tomorrow brings I'll be there...with open arms, and open eyes" - Incubus