I have a friend who recently moved from a Lumia 920 to a 640 and he is very happy with it.
A second baby meant economies had to be made, but the general march of technical improvement means it's more of a side-grade than a downgrade. From having handled it, I can say it feels really nice in the hands, so much so that I was tempted though I run the 930 myself. It feels good and solid without being heavy, so you won't feel you have to curate it. It is not as stylish and sexy as the 735, but I'm sure, having read your other thread, that you'll like it.
You were right by the way to pass on the 930 - and I can say that, because I own one and have not been plagued by 'issues' beyond a reluctance to wake up on double-tap of the screen. Amalthea, for that is her name, is beautiful, elegant, buttery smooth, has an outstanding camera and still catches the eye, but she is also too thick. She does not sit in the hand well and those sharp edges can trip the fingers.
I would say that if you don't want to wait for the autumn, the 640 is the way to go.
Whatever you decide, good luck with it and thanks for asking.