I play a lot of fast palm muting stuff, and I use a Proco Rat to boost my MP1. It works well with the MP1, MP2, Triaxis, but not with my Rocktron Chameleon 2000, wich is a digital preamp. The pedal is actually a Deucetone Rat, that have in total 4 different clipping options, including a clean boost.
I tryed different pedals to boost my preamps, and I compared them with a true bypass pedal switcher. In order of appreciation: Rat, BD-2, Ts-808, SD-1, BBE Crusher, MT-2, Behringer MIC200, DS-1.
1- Rat Deucetone
This is my favorite. I prefer all of the modes of the Rat, to every other pedal I tryed to use as a boost. All the modes have slight different flavors (more bass, more agressive, etc.), but they are all good. It's true bypass, and really doesn't like to have a buffer in front of it. With boss pedal in front of it, it sounded like crap. It sounds tight, really low noise, awesome. Just don't put too much distortion or you'll mess everything ( I set mine about like this - dist-9h, filter-12h, level 3h).
2- BD-2
A bit more warm than the Rat, and have a more vintage/warm vibe to it. Really nice.
3- Ts-808
Sounds nice and natural, just add a touch of punch, but not quite enough for my taste, and introduce way more noise than the rat.
4- SD-1
The less expensive pedal! I could have put it in 3rd place at the place of the 808. More agressive than the ts-808, but more harsh too. That pedal can be microphonic and cause feedback.
5- BBE Crusher
Suppose to be really close to Marshall The Guv'Nor. Doesn'T sounds bad, but it have a 3 band EQ. I don't want to tweak a 3 band eq on my boost pedal! It's true bypass.
6- MT-2
Metal Zone! I have been able to get a not to bad sound, close to the SD-1... But every other settings sounded really bad.
7- Behringer MIC200
It's actually a small mic preamp that can work as a DI. It has a tube in it. I did not play a lot with it because it caused to much noise to be used as a booster for heavy guitar sounds. The sounds "wanted" to be nice, but was just too noisy.
8- BOSS DS-1
I have not been able to have an instesting sound as a booster with it. It's a classic distortion pedal, but I just could not find a way to use it as a booster.
I also tryed about every OD/DS pedals simulation of my BOSS GT-10, but I consider it a different topic
. I don't think I would have tryed a RAT pedal if I didn't have a simulation of it in the GT-10. That's a great tool, but I'm trying to remove it from my rig.