The GMAT is driving me nuts

The long and short of things are, I've been studying for close to a year and I feel like I'm spinning my wheels.

I've gone through several books, including Manhattan's foundations of GMAT math and their complete GMAT series. I'm still studying for math and after bombing the advanced OG DS word problem section, my frustrations have really come to a head.

I'm seeking a 700+ score. As ridiculous as it sounds, I almost think I'll never get there based on the rate I'm going at. For example, I'll go over a specific section in the Manhattan series (say, word problems) then by the time I finish and move on to doing the OG questions, I've forgotten material! Not to mention, there are just so many problems! Between my Manhattan GMAT books, the OG, Jeff Sackman's total GMAT (Which I WOULD NOT recommend, by the way - he makes it sound like it's a comprehensive guide that goes over problems in extreme detail when in fact, it does not) it's a bit overwhelming. It seems that by the time I get a relative handle on the OG questions and move on to others, I'll end up forgetting how to do the OG questions. There is so much material and so many variances on problems, I'm slowly sinking into the belief I won't master enough to get that elusive 700+ (and yes, I realize that no one is going to master all of the material, that is indeed borderline impossible)

I'm currently going through the whole of the OG, marking down problems that I get right and wrong. Once I complete that, I will go over again all the problems I got wrong and will keep doing so until I get them all right. Still, that's a long way from me being prepared. Each problem may have ten or so slightly different permutations, and I need to be able to do every single one. I'm at a loss on how to move forward. I'm not sure buying more books will help and while I do plan on taking a course, that's more for GMAT strategy than actual content understanding.

I'd love to be able to say I can devote hours each day, every day, to reach my goal. Of course, that's not a possibility. I'm spending far more time than just about anyone I know or have read about studying and it seems that my results have been mediocre at best.

Does anyone have any tips as to how I should proceed forward? I'm not going to give up on this, and I will get a 700, but I also want to look for ways to streamline the process so I can stop wasting time and energy on study methods that are not effective.

Thank you