I didn't keep flushing methodology consistent, but I think the results are still worse than 2°C window. Here are the complete results from those tests:

It would be interesting to know "what changed" with Shot 10 and later. Taken as two groups, assuming that "something changed", then the repeatability looks reasonable to me.

Without looking into what changed, it's hard to draw conclusions.

For the first 5 shots I only recorded date, not time of the day, but I'm pretty sure that most were not back-to-back. Shots #1-#3 were on Dec 6, #4-#7 were on Dec 7, #7-#11 were on Dec 8 (all at least 30 minutes apart), #12-#13 were on Dec 9 (30 minutes apart). My conclusion is it's a crapshoot, possibly the result of varying room temperature. I have pretty good insulation at home, so no wild temperature variance. Could thermosyphon stall be at play here?

I'd suggest some carefully controlled experiments where you've got enough measurements under each condition to be statically significant. How many will depend on the variance of the measurements, but I'd guess 10-50 somewhere. Commenting on outliers is "OK", but removing data that seems not to support your hypothesis is bad form. This includes deciding how you're going to "clean" the data after you've collected it.

At least for me, what seems like "random shots in the morning" isn't a well-designed or controlled experiment.

There's been a lot of work like this done before. If you're getting results that are substantially different than those results, checking your experiment design and execution would be the first step, before shouting from the rooftops.

Jeff wrote:Commenting on outliers is "OK", but removing data that seems not to support your hypothesis is bad form. This includes deciding how you're going to "clean" the data after you've collected it.

I don't find it amusing that you suggest I "removed" data. My post from Dec 6 included 3 shots, and these are exactly the same first 3 shots in the table above. I didn't comment further in that thread, but in the next few days I made additional tests (shots #4 to #13), and the overall results were even worse. I could have come back to that thread and "shout from the rooftops" about the issue, but I just chose to move away from E61 (a decision I'm now reconsidering in hope that maybe the performance of my Quick Mill was an outlier). You may want to check the facts before assuming ill intent. I fully accept that my test methodology was lacking. I'm not a scientist, and am open to suggestions on how to improve it. I'm not however willing to accept that there's any bad faith behind my tests or posts.

I didn't state that you altered the data. Selection of how to clean the data to "make it pretty" is a too-common problem. If you recall, I commented earlier based on what appeared to be bimodal data, which would have been hidden had a decision been made to remove those points as "wrong".

I did provide suggestions that improving your experiment would likely be beneficial. I also stated that should you find that your results were significantly different than those that have come before you, examining your own methods would be recommended before announcing your results.

As Jim and Jeff have already said, the temperature profile of a properly built e61 (Bianca included) is literally historic for its repeatability. It may not be a flat temperature profile but with a dual boiler (and a properly calibrated PID offset) it will be remarkably reliable and consistent shot to shot.

You ran some test on your old machine that you're looking to replace with a Bianca. Those tests don't show what is historically agreed upon by many people over the past 60 years. You may want to consider you missed something in your methodology or there may be an issue with that particular machine.

As to the question you asked in the title of the thread, no. The concensus over the history of e61 machines is that owners do not find temperature stability inadequate.

If you buy an e61 dual boiler with flow control you'll have a machine capable of making extraordinary coffee when paired with a high end grinder. At that point the equipment is not the limiting factor. We, as the home Baristas, are.