Sean1983 I saw a youtube video with Rob Chapman and the winners of the metal pedal shoot out were the EVH 5150, the Freedman BE a Diesel pedal and the Boss Metalcore.
Just be aware that here Lee was randomly turning knobs, which is not the best way to tweak a pedal to get a good sound, and there was only a small pool of pedals they went through. With that said the drive pedal market is completely oversaturated so it's difficult to choose.
But the Orange amps should have a ton of gain, and you might not even need a pedal, unless you don't like the Orange flavour of gain (then why buy one), or you want to go from clean to dirty and the amp only has one channel. But I'd always choose tube gain over transistor gain (hint: pedals are full of transistors).
If you want a tube amp get a tube amp. People rave about the Katana but it's known more for its versatility and features than it's amazing tone. A tube amp will have a beautiful quality about it that the Katana can't capture.
It makes more sense to get the amp (and cab?), then decide if you actually need a pedal. And if you do, you may just need a boost (like a Tubescreamer or whatever) to push the tube gain a little further, rather than a distortion pedal.
