It's hard to judge since I don't know how decent you are at maths but I can tell you doing specialist and methods together, makes everything so much easier in methods. I'd say definitely do specialist; it's not as scary hard as you might think it is - it's actually got relatively little content in comparison to some subject that I see my friends doing like revs *cough* *cough* Usually schools finish teaching the content earlier than other subjects like biology, for example, where parts of Unit 4 gets totally thrown outta the window haha
I once heard from a teacher that the reason why it get scaled up so much is not only because of the fierce competition at the higher end but that universities really do want to encourage peeps into doing specialist. It's highly regarded as a standard if you want to do higher maths (y). But of course, I'm not saying that it's necessarily true though.
But this is coming from me. I absolutely adore maths.