the original 7125-3 (2003) had a more through action with strong tip and deep yet firm flex - scandi 420, skagit 450, 45-50' 485 gr head. The original 7127-4 (2007) was more progressive, with a lighter tip to stronger butt, similar grain window, and also liked lighter scandi lines.
Both 7 wts (rated 6/7/8 on the rods) were designed for smaller fish and summer conditions. As angler tastes evolved to shorter and lighter rods, these "7 wts" got tapped to do more including winter work. With this shift and new materials, both rods were updated 2 years ago to get a little more performance and power, while staying light 7 wts (6/7 wts) compared to the typical 7 wt rod.
the 7125-3 is now more progressive and crisp, has a stronger butt and faster feel of the two, and the 3 pc design keeps the quick feel very smooth. The new 7127-4 has a stronger tip, which drives the load deeper into the blank for more flex into the butt. Both have similar grain windows (accurately reflected on CFB website) and cover the same casting range.
I've been fishing the 7125-3 as my go-to rod for summers on the North Umpqua, Deschutes, etc and for coastal Oregon winter 2-salts, while a few close friends ply these same waters with a 7127-4. We can swap rods anytime and get along just fine. So, I'd say both fall in the broad "medium-fast" category
hope this helps