Hey!
Before I say anything, remember its best to decide on your own since you know your own ability. Anyway...
From my experience in year 11, I did English, spesh, methods, physics and chemistry, The two maths subjects (and physics) go so well together, and if you are keen and believe you can cope with the load then go for it, I believe physics and chemistry also go well together so, IMO, you should do physics and either spesh or chem, or both and not do further (I heard its really hard to get very high marks in further) but its entirely up to you. after we completed motion in physics, it came up in spesh (kinematics, which is easier since it has less of those hard questions) and I was all over it, then it came up in methods!
The questions in spesh are hard, but the more of them you do and the more questions you ask your teachers, or AN, The easier it will become.
P.S It is said that if you do spesh, apparently you don't need to study for methods. This is true for year 12 I believe.
Like I said at the start, you know your ability, so if you believe you can manage then I say do spesh, but if you think another way will be better for you then do that.
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Oh sorry, your going to do further 3/4 in yr 11, i also forgot to say, if you really enjoy maths or your faiely good at maths then do spesh methods and physics since they are like one subject!
mod edit: merged posts