I'd be very careful on ebay for fakes. Just make sure they can be verified as authentic. I play AP2 710s and really like them. There's not much difference between the 710s and 712s, but it looks like those are the original and I think there were some decent changes to the 710. But I'd go see if you can hit some 712s somewhere like Golf Galaxy or Golfsmith with an X100 shaft. They should have similar feel. If your shaft is too soft, you'd likely be hooking the ball, or at least most of your misses would be left. If you're spraying it to both sides, I don't know how much a stiffer shaft would help.
But it sounds like you're a really good player, so you may be able to go the X100 route on your irons. A lot of amateurs, from what I've read on club fitting sites and forums, who have a really high swing speed with their driver don't have the same with their irons, but you could be an exception to that. If you're swinging fast enough to hit X-stiff shafts, it's possible the best thing you could do for more consistency is to slow it down.
But that's more Kyle's department. The most significant change I ever made over the years was to slow everything down. When I was able to that, that's when I went from 20 HC down into the mid-teens almost instantly. And since then, I've been able to work on my game and improve more effectively. If you have natural power, you're lucky, but one of the things with natural power is that you don't have to swing "hard" to generate club head speed (i.e. Ernie Els).
I've always found DG shafts to be a bit boardy, but they may fit your game. If you do nothing else, I'd definitely try to demo different shafts. I was amazed at how much better the KBS shafts felt. I played them for 3 years and absolutely loved them. In my current set I have upgraded Nippon shafts that are also much smoother than the DGs or PX shafts. But you have to figure out what fits you best.
I wouldn't buy clubs without at least trying some out first. That kind of deal will still be there. But I'd worry more about the shafts than the clubhead. At least that's what's worked best for me.
If you really want to learn about golf, fitting equipment to your game (all the difference specs of clubheads shafts, lengths, etc.), or clubmaking I'd start spending some time at
www.golfwrx.com. It's far and away the best golf forum anywhere and it has a lot teaching pros, clubmakers, and just very passionate and knowledgeable golfers. I've learned more about equipment and golf from there than anywhere else. They have several forums there for all kinds of golf-related topics.
They also have a buy, sell, and trade forum. That's where I've bought used clubs over the last couple of years with great success. Those who sell equipment there are well known in the community and have to pass certain standards to be able to sell there. It's mostly people in the golf business. You can get great deals there and can rely on the quality of the clubs. You can but shafts, clubheads, clothes, teaching aids. Spend some time there before you decide on a set to buy would be my advice.