Proper leather shoes

No. The general rule of thumb is that 1 size with up is 1 width down, viz. 8E has roughly a similar hold to a 9D.

In which case it follows that the 9.5E will have a similar-ish fit to my supposed ideal, a 10D?

My 10D plain toes are good in width but quite long. The 9.5D longwings I have have plenty of toe room, I would say at least 2cm.

Thanks for your help with this, much appreciated.