Has anyone heard the Ref 3?

Yes, that sounds like a better description - ruthlessly accurate. The tubes had just over 400 hours on them, so I assume it's well into the break-in period.

I read in another thread here last night that there's an upgrade to the LS25 due soon (LS26) that takes a lot of cues from the Ref3 in terms of sonic quality.

Over the past week I've had the LS25mkII and Ref3 in my system, as I'm looking to upgrade my SP16L. Sources are a hard drive feeding an ARC DAC5 and a VPI Scout feeding an ARC PH3, and an ARC VS110 drives my Totem Hawks. I'm very happy with my system, but I'm looking for upgrades that make it sound "bigger".

Like Zargon, I found the Ref3 to be more detailed in nearly every respect. However, in the context of my system the LS25 had a far smoother and more balanced sound. It sounds to me like the rest of Zargon's system was up to the standards that the Ref3 sets. For me, I'm probably going to wait a while because I feel that the Ref3 can be ruthless.

Hmm, is ruthless the right word? Perhaps not, maybe unbalanced is better, but regardless I'd recommend thinking carefully about the context you place the Ref3 in otherwise you may find yourself in rapid upgrade mode to bring the rest of your system up to what this amazing preamp can do.