SC = you already have MGMAT SC
which is the best, don't need to read others just adds to the confusion.
RC = try Princeton Review verbal
workout for the GMAT but skip the SC portion since you already have the strategy from MGMAT.
For me, I use the "grocery store" method (discussed in this book, get what you need and get out), I jot down some quick notes on what's contained in each paragraph. No more than 2 short sentences. Basically telling me the vibe of the author's tone and a layout. I hate Science RCs but even with these I use this method and I usually get the questions right although I have no idea what I've read.
I think the biggest mistake in RC is taking too many notes and focusing too much on details - it's unnecessary.
Good luck! Hope it helps.