How long can I ask an agent to wait?

Here's the situation: Sent out a bunch of queries and got a great response. From the 25 or so queries, half a dozen top agencies wrote right back asking for the proposal (non-fiction). This, in mid-August. One of the agents asked for an exclusive, but when I explained that I already had proposals out, he said, "OK, but give me your word you won't sign with anyone for three weeks." I thought that sounded reasonable, and he's very well known and was pretty enthusiastic about the project.

A week later, another very respected agent offered me representation. I wrote to her explaining that I had to wait two weeks more before I can make a final decision, explaining everything to her.

Was it a bad move to be so revealing? Is it insulting for an unknown, first-time author to ask a big-time agent to hold on for a couple of weeks while I check out other options? My thought was that I want to be up front from the beginning, but after sending the email, I started wondering if maybe I should've just dragged my feet a bit instead of explaining.

Any opinions?

Thanks.

Thanks for your thoughts. I just told everyone holding my proposal that I'd be deciding in two weeks. Some seemed grateful that I'd told them, others a bit miffed. But it's one of those natural filter situations: I really wouldn't want to have a long-term relationship with someone who's gonna be bitter about other agents' interest and my need to make a careful choice. They sure know it's a business on their side, so why should it be any different on ours?

Now we've got interest from an editor at a very large house, so maybe we'll do it without an agent at all. That feels a bit risky, but I'm not sure...

Anyway, thanks for your thoughts and congratulations. I sure didn't expect this a few weeks ago!