If verbal is your weakness, esp RC, I don't think the latest OG would make that big a diff. I would get Verbal Workout from PR, along with Cracking the GMAT
if you don't already have it. They have the best verbal prep and really good answer explanations, so you can figure out where you're going wrong. I have both books and would definitely recommend them.
If you've exhausted the 10th edition of the OG and want more practice probs, then yeah, get the 11th edition (you can probably get one on Ebay for a song), but Verbal Workout has like 200 questions, so that might be enough.
Hope this helps...