My Audax runs 32 spoke Ambrosio rims - very similar to open pro's I then run 25 or 28mm tyres at 80 psi front and 90 back. Frame is Reynolds 631 OS (28.6 28.6 31.7 .8.5.8)
Regarding front end comfort, the road shocks will travel up through the tyres, wheels, fork and bars to your hands. I cannot see how the frame will make much difference to this except perhaps the head tube supporting and reducing flex in the steerer tube.
I suspect that rear end comfort is mainly down to tyres, wheels, seatpost and saddle with the frame contributing - but maybe not much.
Recent experiences with an alloy frame - which I sold as it was so harsh, may have been mostly because of the stiff, over size bars and cheap alloy seatpost. I suspect the straight bladed, monster size, disc forks didn't help either.
So the frame I am building - (Double OS) should be comfortable to ride as long as I select bars and seatpost carefully.
So I am going to keep a look out for some NOS Deda 215 26mm bars - and a girvin flex stem
I would like to make my own tapered titanium seatpost but suspect this is beyond my capabilities.