Just my .02.
I really like the more traditional geometry of the SLR over the GF. The sloping top tube of the GF is doing nothing for me. But the GF’s impossibly thin seat stays are sweet.
The GF has the thin seat stays and 412mm chain stays over the 402mm chain stays of the SLR. That also will give you more options for tires on the GF and probably the main reason for a softer ride.
All in all, I think you may like the SLR better because it is more like your current ride. While the GF may seem “squishy” right now, you can change your riding style to accommodate the greater flex and take advantage. Personally I like a bit more flex when climbing, it makes for a pleasant (for me) pedaling rhythm.
The only place where I prefer stiffer is in a field sprint. I’m not in many fields sprints. Actually none. Except in my head. Then I always crush the field. 