Query Letters–How much is enough?

I’ve been getting some more query feedback and found something I’d never heard before: 
Only describe the first act, or maybe only the first 50 pages.
This came as a complete shock to me. I’ve been through Writer’s Digest webinars, 3 conferences, and a ton of blog posts, and never once had I seen this advice. All I’d heard was “don’t give away the ending–that’s what a synopsis is for,” and “do include voice so we understand your writing style.”
So is it good advice? I went digging, and came across several pages supporting this advice:

So why only Act One? The goal is to hook the agent to read or request pages, not to tell the story itself. And if you get into telling close to the climax, fitting in voice becomes much harder. Plus you lose so much, trying to do this in a single page (more on that later), that the coherence of the query letter disintegrates (at least for some of us…<cough>).

Edit: I mentioned this to someone in the industry, and this came as a surprise to him. He recommended erring on the side of showing more than the first act. Rationale: it’s important to convey that you can tell a full story.

How many words of story?

I’m still not sure how many words of story to include. I’ve heard wide-ranging, conflicting advice here:

  1. One paragraph intro (personalization/title/genre/word count/comps), one paragraph story, one paragraph bio
  2. Whether to include the log line with the story: yes and no
  3. Whether to even include the bio if you have no writing credits: yes and no (and if yes, typically it’s make it very short and story-relevant).
  4. Intro, 100-200 words story, bio
  5. Intro, 250 words story, bio

It’s all over the map in some regards. Mostly I heard “shorter” from agents, and on the longer side from writers. I’m beginning to suspect that agents hate reading long query letters because they have mountains of slush, whereas successful writers have often found success with somewhat longer query letters.
I rewrote my query letter with just Act I, and found I was able to fit in motivation and even voice much more readily.