That is incorrect advice. If a pickup is high gain it is NOT suitable for the neck position (traditionally) because the in the neck location, the string is "louder" because the vibrational pattern is larger.
In my opinion, Dimebag is a sellout when it comes to gear. He swore by his Dean guitars, and then had Washburn make and sell "Dean copies" Dean was out of business at the time so I guess it's okay, but then he also swore by the Bill Lawrence pickups until he had Duncan copy it. He sells wahs, and other things, too. I don't want anyone to argue with me on that because this is a pickup forum and I'm only saying it to illustrate this point. In my opinion it is overpriced so he can make his money. He is a paid endorser now, and gets either a percentage of each sale or a lump sum with bonuses at sales breaking points. Unfortunately, this creates a situation EXACTLY like yours! You could replace BOTH of those crappy RG pickups with quality products for the same cost as one which pays him his royalty. By the way, I don't mean he's evil for doing so, either. If I could profit from my name and put out a good product I'd probably do it, too. The Dimebucker is a quality product. But my recommendation is to outfit your guitar with 2 new pickups. It gives you more for your money, and the "appropriate" people are profiting: The pickup makers.
The Steve's special won't sound like the Dimebucker, but it will be a quality sound that you will like. Plus, most of that chainsaw sound is at the preamp/fuzztone level. So in my opinion, you'll find it much easier to simulate Dimebag's sound with the Steve's Special, than to simulate Petrucci's sound with the Dimebucker.
Sorry about the huge rant when you just wanted some pickup advice,
but I think I've helped put things in perspective. Also, if you can afford both, they are perfectly compatible. You can almost always mix passive pickup brands with no problems. Whether you'll like how they compliment eachother is an individual thing, but they will operate fine. Another great compromise would be to find a new or used Bill Lawrence. Most of what you're hearing was recorded with that pickup, not the Dimebucker!