Jo, I feel your pain! It is so difficult to distill a huge book into a one page pitch. It's a different creative process from writing a book. I've only written five queries, but I've *rewritten* them probably over a hundred times!!!! I think I was close to tears at one point myself. It's hard not to feel like a moron about the whole thing (well ok, maybe that's just me!).

Writing a good query letter takes time. I know you want to get it out to agents as soon as possible, but it might help to put it away for about a month--or more--and just think about it. Think about it when you're away from the computer. The one I'm working on now has taken me about 8 months of on and off work (well, I started it while i was writing the book). Like you, I also sought feedback. I think it's my strongest query yet because of the extra time I took (but it could be that the story is easier to distill???).

It's hard to hear sometimes, but good advice can improve a letter dramatically. For me, it helped to step away and clear my head. FWIW--your mileage may vary.