SC is literally mechanical and so it is the portion where you can improve the most...
This is so because in my opinion, grammar can be taught whereas RC or CR is...well (although you can improve on it...) pretty much intuitive... Of course, pratice makes perfect but you wouldn't see a huge jump in score in RC or CR than you would in SC.
My questinon is, what is your average percentage correct on SC problems? Like up to what level do you increase that ratio before you take the actual exam? I read those who got 750+ has great % correct on SCs...like 96~98%. They'd get all SCs right on the exam...
I'm a non-native English speaker but I've studied grammar and feel pretty confident on SCs...still, I find that at times, I rely on the "sound" to help me when I cannot find the logic behind it... Maybe that's why my % correct is 80~90%.
I don't think I'd be above 90%.
How do you approach SCs?
I've found dwivedys to be a SC master.