I’m not sure what a realistic improvement might be, as stated above, it’s all very individual. Important to note that progression won’t be consistent or linear - you’ll have plateaus from time to time. You are looking at a ~40% improvement which is quite a lot. Be patient, you might be able to hit 3W/kg but if you want to stay there then you really need the base to support that.
Also don’t just focus on FTP, work on your weaknesses as well, see the various “Why are XXX so hard?” threads. We all struggle on something, don’t just push the ceiling, pull up the floor as well.
I’d stick with a repeating SSB pt2 and a build plan rather than look at a speciality plan - they are really for putting the icing on the cake so to speak. Don’t just wait until the Ramp Test to modify your FTP, it might be that you find all the workouts easy (or hard) so be prepared to adjust things by a couple of percent.