A 680 is still a great score (though I know you wanted that 710) - congratulations.
I disagree about CR and RC - I absolutely think you can train your brain to get better at logic and comprehension. It's not easy...but it can be done.
For instance, what are the similarities among Find the Assumption, Strengthen, and Weaken questions? What are the differences, and how does that impact how you answer each type of question?
Did you know that one common trap on CR is for a wrong answer to have exact wording from the argument--but the words are put together to convey the wrong meaning--while the right answer uses synonyms and does actually convey the desired meaning? Lots of people will then narrow to these two but not be sure which to pick (because they're feeling that they've already spent their two minutes, so they need to answer NOW... and so they don't read carefully). They end up picking the one with the exact word matches... and getting the question wrong.
You can absolutely learn all of these things and how to deal with them. You don't even have to figure it out for yourself - the lessons are out there. (See below.)
If you think that's not possible, though, then you probably won't get much better at those areas. In other words, it's a self-fulfilling prophecy...
Here are some SC resources:
http://tinyurl.com/scprocesshttp://www.manhattangmat.com/blog/index ... orrection/And CR and RC, in case you decide that you're interested after all :)
https://www.manhattangmat.com/blog/inde ... reasoning/https://www.manhattangmat.com/blog/inde ... rehension/Also, read this (it talks about how to study overall):
http://www.manhattangmat.com/blog/index ... -the-gmat/And come back here with any questions!