Don't believe everything you read. You need to hear things in your system and not go by reviews. In my system the LS27 does not outperform the Ref 3. I have spent a bit of time with the LS27. A few years ago I owned a LS25 mk2 and wanted to upgrade. I tried a dealer demo LS27 that I could get for a very good deal. I passed because I did not think it was really much better than my LS25 mk2. I also have had the Ref 3 in my system. It was clearly better than both my LS25 mk2 and the LS27.
I currently own a Ref 5se. It is infinitely better than any previous Audio Research preamp I had heard. And I have heard a lot over the last 30 years. When I first borrowed the Ref 5se I knew it was special. After a week I knew it was not going anywhere and bought it.
The tubes in the power supply have an affect on the sound. You can hear a difference just by changing the brand of 6550 in the power supply on the Ref 5se.
If you are looking to upgrade I would highly recommend auditioning the Ref 5se. IMHO the LS27 would be a sideways move at best.