Dude, you just said Porcupine Tree and Steven Wilson! That settles it: get the Sierra-2!
You've no idea what you've been missing via your previous speakers. If you go for that kind of sound, and groups that care that much about their recording quality (if only everybody did! What a utopia that would be!), then you owe it to yourself to hear what their recordings REALLY sound like via a pair of Sierra-2!
I know you're trying to find a way to stick with your original plan. I get that. And, believe me, if I thought it were the better choice, I'd be telling you to get the Sierra-1. I am not a "one size fits all" sort of person when it comes to recommendations. I strongly believe in suggesting the right product for the right situation.
With what you just said above? It really couldn't be any clearer which way you should go. The Sierra-2 are your speakers. I can't stress enough how happy you will be when you hear them.
I don't know if you've ever had a dog or cat. If you have, I'm sure you've had a time or two when you've got the TV on or some other sound source while the dog or cat was in the room. Most of the time, they just ignore the sounds from the TV. But, every once in a while, you'll see them wig out a little bit, and totally prick up their ears and stare REALLY intently at the sound source. It's like, for whatever reason, something they heard really got their attention -- haha.
Well, that's what it's like when you hear an excellent recording via speakers as good as the Sierra-2 -- except it's for us humans
There's just this uncanny realism that cannot be conveyed any other way. It's the difference between, "that's a really good pair of speakers" vs. "that just sounds REAL!"
There's just something extra that goes off in your brain. Something that says, "that's real! Holy crap. This is awesome!"
Yeah, you've gotta get the Sierra-2. I've rarely felt this certain about a tough decision. But, it is 100% the way you should go