You asked about floor plans but remember there are other significant differences between the RT-25 SC and the RT-25 Classic.
Classics had Yanmar 110 hp, Yanmar 125ish hp, Yanmar 150 hp and Cummings 150 hp engines. The older SCs had the Yanmar 150 hp and the newer 25 SCs have a Volvo 150 hp power plant. The different engines offer different performance and different maintenance issues. I’m very happy with the performance from our 150 hp Yanmar.
Another difference can be in the electronics used. Older Classics used Raymarine hardware. In about 2009 RT switched to Garmin electronics. And in about 2010 the Garmin Autopilot became an option.
Fabric upholstery and vinyl used on the Classics and older SCs (as well as on 27s, 29s and 31s) has been an issue. Many, including us, have needed to reupholster all the seating.
Regardless of model, IMO it’s wise to get both a marine survey and mechanical survey from qualified inspectors.
I’m sure other folks can chime in with other important differences between the 25 SC and 25 Classic.