That's why I am looking at other factors coming into consideration when deciding to buy those 2.5mm shorter cranks - with used BB included (on ebay for some 100 USD). You and the other posts just confirm what I was thinking, how much difference those 2.5 mms can make... but it is move in the right direction
I am thinking I could pass these 172.5 mm cranks to my old bike (with that used BB that would come with those shorter cranks), wouldn't need to put them on shelf or try to sell them. There is a chance it might fit, the frame is from mid seventies (but everything on it is of later date), still decent, with threaded BB (with square tapered axle, cups with balls in them... and 172.5 mm cranks, so that would be no change.
But the new 39T ring would be smaller which would be welcomed, I think I have perhaps 42T small ring on that bike. But finding out if it would fit will have to wait until it is possible to fly back to EU. I would still use that bike when I need to lock it someplace in town, couldn't do that with this new bike.