Right. I read that the Rem. 540 has a lock time of 1.4 ms., which is very fast. According to another source, the British Paramount action has a lock time of 1.3 ms., which has been described as the fastest of any production action.
And, Tim, as you say, the Anschutz M54 action has a very fast lock time. I read that, depending on the model series (1400, 1800, 2000, where some adjustments were made along the way), the lock times were between 2.3 ms. (1400 series) and 1.5 ms. (2000 series). I've seen 1.7 ms. for Anschutz M54 as well--probably what you see in the 1700 and 1800 series. As you and Slick Willy say, this is not an important factor in rimfire BR, but could be in position and silo shooting.
Are there any Win. 52 shooters here? I'd be interested in knowing what Winchester was able to get the lock time down to in their speedlock versions.