Size wise, CFR707 has longer reach and top tube, it’s also heavier. Although the BSA is great. I’m buying frame for a person who use size 47 at the moment. And I don’t think it will fit him. I saw you have experiences with CFR505. What do you think it compares to GR029 in terms of long distance comfort? How do they feel, compared with other big brand names you had?
My CFR-505 is my go-to bike if I ride more than 300km, not because it is more comfortable than my Canyon Ultimate CF-SLX, but because it has all the screws for bags
I don't know the GR029, but comfort comes from a relatively flexible seatpost(27.2mm) and low pressure tires(eg: 2.5 or 3bars for 40mm tires).
The frame has little to do with comfort. The two triangles of a frame are stiff enough for most of us.
Geometry plays a role too if the rider is not very flexible anymore.
Maybe a shorter stem and spacers, or horror... a reversed stem
may bring the handlebar where it should be for your friend on a 707 ?