Thanks for your replies. I remember being on a tour event many years ago and climbing a pass out of the saddle in the drops the entire way, being reasonably comfortable and in rhythm with it, and making what seemed like good time. But this really doesn't tell me anything!!
I have no times or anything to compare it to. I just restarted riding alot again a couple of years ago, but I haven't really tried climbing in the drops again for any length. In my head, I have just assumed that if it was a good method for steady climbs, there would be more people out there doing it, but perhaps it is really a personal preference thing, and I should just experiment with it to see whether I can actually do any better that way---or whether I can even comfortably hold such a style for any length of climb anymore.