I have a midrange system (Alienware M11XR3, i7, 8GB, NVidia 540M). A while ago, I started having similar CTD problems. This thread chronicles my journey to a solution.
http://www.subsim.com/radioroom/showthread.php?t=205755 I hope you have solved your problem and can enjoy GWX uninterrupted, but, if not, maybe some of the things I learned about might help you. (Or someone else!)
Good luck and good hunting!