Anyone have user experience with the two product lines? What are the practical differences? Are the Performance line MTB tyres made of "soft" rubber, that provides superior grip?
A simplified way to think about this is a tire has three core attributes: performance, durability and cost, but you can optimize for only two of them. That, and marketing, is what seems to be afoot.
Schwalbe's web site has some general information on the construction of tires. A takeway is they can tweak the rubber compounds to improve a tire's characteristics for specific needs. Their very high-level/marketing view list enumerating compounds equates the "Triple Star" compound as the best family, but it's tuned the specific user type mountain (grip, speed), road (speed, weight) and touring (durability, fewer flats) use. It's not that different from 105/Dura Ace vs XT/XTR.
It may be more helpful to consider their suitability ratings within each category. For example, under the All Mountain, the Nobby Nic (with the PaceStar, the high-end compound) is touted for its grip in soft surfaces and decent on hardpack/loose. Its other virtues are comparable to the Rapid Rob (standard compound) at approximately 60% of the cost. Thus if grip on soft-pack is really important to you, you might be willing spend more. Skimming through their touring tires, there does seem to be a tradeoff between speed/grip and protection/durability.
Schwalbe's breakout seems reasonable, though I'd like to see some comparables with other vendors for calibration, ideally by the folks at Bicycle Quarterly who have done work trying to quantify aspects such as inflation pressure vs tire width.
Hope this helps.