I currently have a Ref 6SE, prior I had a Ref 5SE and have listened to LS27 and LS28SE.
The Reference series is definitely a step up in sound quality, just like the LS28 SE is a step up from the LS27SE. I’d say the LS to Ref of the same generation is a bigger step than one or two generation steps in the same level.
So after yours is the LS26, LS26SE, LS27, LS27SE… etc.
The Reference series is cut from the same cloth as the LS… exactly… so same tonal balance, midrange bloom etc, but generally better in all qualitative qualities, noise floor, dynamics, imaging etc.
The decision would must include consideration of your other equipment and future of your system. If you are looking long term, then regardless of your other equipment the Ref would be a good decision. If you are mostly concerned about cost, then maybe an upgraded LS would suffice for you.
It would be very helpful to see your system. This is very helpful for us trying to help. There is a place under your ID to place some quick photos and ID equipment under Virtual systems. You can see mine there.