I think OG should be used more as a tool for understanding different question stems or getting used to the type of questions which *might* come on the actual test.
i wouldn't really say that scoring too bad or too good would give you a great indication of the score but it will give you an estimate about your preparation. It means the score wont tell you if you're gonna get a 740 or a 720, but i can tell you that you're prep is of level above 700 level or not.....
On using the OG10, if there is a substantive difference between something in OG10 and something in OG12, then GMAC must've made that change for a reason. If they strip something out that used to be there, that's typically because they're not writing things in that way anymore. So the use of OG10 would be best for practicing and not getting used to the format.
*the above mentioned opinion is what i think, it's not official, so you're free to use/discard it

. I really hope it helps*