My title tags in SERPs show only about 520px instead of 600px max

[deeper]

Hi,
many of you may know it: The length of the title tag shown in SERPS is max. 600px, it's not dependant on number of characters. Every expert knows this and every online tool checks the 600px.

But, surprise surprise, most of my title tags, which are 500 to 580px, are truncated! All online tools give me "green", but they are actually truncated. Checking the SERPS with other keywords and title tags it confirms me that Google only shows about 520px at best.

Has G changed their 600px maximum or increased the font size? Does anybody know?

deeper

[RedBar]

600 pixels approx equal 70 characters and is considened max display width.

Just because this is the maximum, or was, the display width, whatever else is in that ttile is still taken into account surely even if it is not displayed? I don't know, enlighten me.

FWIW I very rarely use more than 50 characters and that includes the company name, overloading the title can have an adverse effect in my experience, however I do comprehend precisely why newspaper sites do it or sites wanting to fully explain "complicated or lengthy" subjects.

[deeper]

@Robert:
Thanks for your comprehensive post and your thoughts.

All checking tools do know about the pixel limit and that there is no character limit, but strange enough some of them cut off the display beyond 70 characters, even if for example 73 characters only need 535 px.
I don't know why some tools follow this non-existing 70 character limit. As pixels are relevant, it makes no sense, but the moz tool seems to do it right, i.e. only considering the pixel length.

Let's take the example which the moz tool shows completely, without any drop:
Professional holistic and psychological therapy of serious diseases

Not important, but this are 67 characters and - more important - only 531px. The tool displays it completely. So far so good and no surprise.
However, and this is the reason for opening this thread, G drops the last word "diseases"!
All title tags like this, with 520 - 570px, clearly below 600px, are shortened by G in the SERPS.

You may check it easily by just searching with any keywords and checking the pixel length of the longest titles which are shown completely in SERPS: You will detect, there is no one with more than 520 (525?) px.
This may be due to any recent change, like it is mentioned here on Twitter:
[twitter.com...]

So there seems to be any new limit or the same limit but with a bigger font, what JM supposes.
But noone knows for sure if it is just a test or if it will remain and what exactly has changed.

Sure, having really long titles (adding cancer...) the title will be shortened and show this ugly ellipsis. You may pay a price for having added words indexed.
But titles with 530px having truncated, this is new to me. Is it also new to you?

Another issue: You say one has to consider bolding of keywords in the SERPS-title, which needs more pixels than without bolding.
Has G recently returned to do this? As far as I know G stopped doing this some years ago and I still do not see any bolded keywords in SERPS. In description, yes, but not in the title tag. Or is it different due to country/language?