GRE is good. In fact, it is harder - mainly because of the verbal comparison section. However, as for RC, they should be similar.
I'd say that you read a lot (like I recommended in another thread for a non-native speaker). The key to RC improvement is your reading speed, which correlates well to your size of vocab and your understanding of English syntax. Typically, it would be advisable that you finish a CR stem in 25 seconds. That way, you'd be able to finish a RC stem in a little more than a minute. But sometimes you act like a CD-ROM reader that searches for a specific track of the disc (the article, that is) - you want to find out which word means which, which sentence has what significance. Most of the time you can use control + F function to find the wanted section, avoiding reading the whole thing.
Some may disagree with me, but SAT RC, GMAT RC and GRE RC do correlate with each other very well. GMAT is in fact one of the easier ones - for me at least - since it is presented on a computer screen from which I routinely read my newspaper every day.
I read most guides for GMAT RC : the dedicated one from Manhattan GMAT
as well as the one included in the PowerScore verbal bible
. Both are pretty simplistic, without much specific guide. The only caution both guides give is that you should read the articles carefully. This is unlike the SAT RC, in which you blitz through articles, looking at only the first and last sentences...because SAT articles are Soooo much longer and so much more annoying (there are two passage comparisons involved). In fact, I recommend that you read Rocket Review Revolution http://www.amazon.com/The-RocketReview- ... 0451213114
if you have trouble with speed. RRR is the best of the best RC guide that sends numerous SAT contenders towards the 800 RC (and Harvard Yale Princeton Stanford also). I can totally vouch for this book, written by PR's founder Mr Robinson. I bought the book for $20 and can still sell for $60 at the moment (the book is out of print). It's much more reliable than either the GRE book or the LSAT book which I'm gonna discuss further.
if you want to go hardcore, go with PowerScore LSAT RC - but in my opinion highly unnecessary. In addition, the LSAT guide has a huge part advising you how to mark up the article with VIEWSTAMP indicators, which cannot be performed on the computer screen. I did some LSAT prep alongside my SAT prep last year, and I found LSAT RC a somewhat longer version of CR - intense monstrous CR, the type of CR that has a lot of logic twists. GMAT RC is somewhat closer to TOEFL RC.....if you want to get a feel of TOEFL RC, go take a free test. They're very straightforward, and should be cakewalk for you if you've been speaking the language for at least five years.