Spesh is very similar to methods. It's pretty much built around calculus and is a natural extension of the functions and calculus you learn in methods. Also the probability and statistics you learn in methods is useful in this study design as there is a bit of statistics in spesh now. Complex numbers and vectors and really the only non-related units, but even vectors tie in to calculus eventually.
Spesh does also have a bit of physics. The kinematics section of the course does have its roots in methods as an application of differentiation and integration, but does get more like physics are you throw in some constant acceleration (suvat) formulas and differential equations. I imagine this is also the same with mechanics, but then again both of these topics integrate well into the greater calculus/vectors slant of the course.
Ultimately, I'd highly recommend spesh. It's challenging at times but also a lot of fun. If you are good at maths and enjoy methods, you will also enjoy spesh. The physics aspect of the course isn't too prominent either.