Hmmm..
Rather than specifying the Tab's maximum width by filename characters ('max character width')...
..Perhaps a secondary option for specifying width in
pixels too and let any longer filenames than that width truncate to the pixel size.
I made this small video on 'tab size jump' with current 'max character width' solution (normal behaviour, not a bug):
Related topic;
http://newsgroup.xnview.com/viewtopic.php?f=62&t=21542
So I could suggest a secondary option as I think that a lot of users are satisfied with the existing 'max character width' solution and for this not be fully replaced but complimented with a secondary option.
I then made this quick UI mock-up to show what it would look like:

- Untitled.png (2.99 KiB) Viewed 4857 times
Settings>Interface>Tabs
So default pixel size could be '170'. Additionally, perhaps by default, the setting would disallow user-specifying less than '100' pixels.
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This is not an important feature for now, but for future

Thanks for reading.