At first I would like to thank you all for your priceless help. Each of your advices contains valuable for me informations, suggestions, and I believe that what you wrote may be of good use for others, who will, perhaps, be facing similar problem.
Your advices let me to make a plan as following:
As this instrument is a fairly new guitar in my hands (I bought it on September 4th of this, 2012 year, and I did not play it for a period of one month (October) I will begin from following advices by Michael.N and John W. Pierce - jwp. Another words: I will strongly concentrate now on playing/practicing at this 40 mm. string spacing for ca. two months. As jwp said:
…give it a few months of practice; at worst your left hand fingering will become more accurate. Then if you still feel you want the spacing wider, change it.
I think that I will return to the subject in ca. two months from now.
If after this ca. two months period I will decide to return to the subject, I will follow advices by Trevor Gore, Les Backshall, Douglass Scott, including every detail that helps with finding proper position for the nut. The advices on making longer nut in order to move it to sides in order to find best position, and beginning from moving the existing nut to sides in order to find out the minimal distance from string to edge of fretboard are so simple and wise. They simply make sense. Of course I will take care for the distance from the string to edge of the fretboard measured at XIIth fret (thank you, Douglass). The fret ends are not beveled too much, they are, as I see, just nicely rounded at ends. And I am grateful for mentioning, that the low tension strings should not make problem.
Of course I am aware that eventual change of nut may bring necessity of introducing other changes. But first things first, and then I will see.
The post by OldPotter is, in a way, a kind of "light in the tunnel" for me. What you, Kind Sir, say: …I find that small changes at the nut do make a big difference to the "feel"…
sounds in my ears like what Ramon - Prominent Critic said already: …it doesn't make much difference, though there is some
And I believe, that, in a way, it is in my case what is called "hitting the nail in the head". Just a couple of days ago I found in one of local musical shops a cheap classical guitar with nut of 50 mm. width and e to E spacing of 41.5 mm. And I was nicely surprised because this tiny difference allowed my LH fingers to operate much more accurate, even the cross section of the neck of that cheap instrument was, say, far from what "tigers like the best"
So now I have a plan, I know what to do. And this was fairly easy due to your, Dear Friends, help.
Big Thank You !
PS. @ Kintla:
Dear Sherman: yes it is possible that the entire satisfaction will not be mine. And of course I am aware that I will be able to reinstall the old nut. But I take all this as challenge, and it makes me to feel young again…
Antonio Picado, model 60, 2015, Cedar/IRW. Scale 640 mm.