All the Rat family distortion pedals sound almost exactly the same. The Rat has a LOT of distortion, but I would consider it to be more of a midrangy, thick, lead sound than what you're looking for. The reality is, the longer you look for the super-heavy, scooped-mid distortion pedal, the more you will want a Mesa Boogie Dual or Triple Rectifier amp... that's the sound you're looking for. I have a ton of distortion pedals, and alone, none of them get "that" sound. The problem is that all the pedals that have the amount of distortion you want (a lot) tend to be fuzz type distortions... aside from the Rat... and fuzz pedals tend not to be good for really tight, fast picking on the E string. For example, the Big Muff Pi is great for that loose, superheavy sound that's all over "Siamese Dream," but Metallica's sound (from Justice on) is all about the Mesa Boogie Recto series.
Actually, one of the heaviest, phattest distortion sounds I have ever heard in a pedal is a sound on the Line6 distortion modeler, I forget what it's called, but it's a sound Line6 made that is just insane.
Didi you try
http://www.tonefrenzy.com/2/5gear.htm for sound samples? They have samples of a ton of distortion pedals. Good luck, and please post here if you find the holy grail distortion pedal, we're all looking for it.