As I mentioned in an update in the comments to the previous post, I snapped off Query Letter Version 4.0 last night to an agent with a reputation for quick responses. I woke up this morning to a request for a partial. So -- woohoo! Version 4.0 is working...so far!
UPDATE: Of course, now I'm afraid to look at my e-mail, terrified he'll take one look at my first few pages, say, "What load of crap is this?" and reject me. (How's that for self-confidence?) I want this heady feeling to last at least a couple of days.