This chart is from LS1 Tech, a gentleman was kind enough to plot the differences between his D1SC spinning to 62,000 vs D1X spinning to 62,000. The D1SC does come on sooner than the D1X, but the D1X makes boost more efficiently beyond 5,500.
Having owned both blowers myself on different applications, I can honestly say I feel the D1X is the better bang for the buck
I picked up my D1X as a 2nd hand (really 3rd or 4th hand) deal for this application. If it wasn't for the fact that it's strapped to a fairly large displacement engine, I would have traded it away for a D1SC months ago. The D1X is absolutely brutal from a roll. And I like it a lot
I do miss the D1SC in terms of low-mid curve grunt. Obviously not as punchy as a PD blower, but you knew it was there. We often cite "what rpm are you going to spend more of your time" but the real question is, what kind of power are you looking for when you get there? At WOT, I promise everyone spend more time between 5,500-7,000rpm than they do at 2500-4500. If you spend more time at 2500-4500 at WOT than any higher RPM, then you're buying the wrong type of power adder, you want to look at a PD blower.
That said, yes the X is the peakier blower, but you do not need to rev to 7,000+ to make use of it. With proper pulley combos, you can run a centri efficiently at any RPM. If you have to spin the blower beyond it's max rating, you should just move up to the next head unit if you want more power. If you roll over to LS1 Tech and read that whole post, guy is only reving to 6700 engine speed to hit 62,000RPM on the D1X. At that point, you're going to be fighting an IAT battle. Beyond that, you're exceeding ATI's efficiency rating for the head unit. Not to say that you can't take it beyond that, but the further you go the more you're just french kissing an angry dragon.
What you can't get in a D1SC is the efficiency of design. The D1SC is going to run hotter and never touch a D1X. Apples to Apples, a D1X is the better head unit. IMO, unless you're application is a truck, I think the X is the way to go. I know OP is talking about a P1X vs D1SC, but even the P1X is still the superior design and will take you to max power more efficiently. And again, how high the engine is capable of reving isn't near as important as how much air the engine can efficiently move. The X series wasn't designed for high rpm applications, it was designed to operate more efficiently at high rpm. As in, the head unit itself at high RPM. You can pulley a head unit so it maxes out long before the engine hits its peak, but then you're overspinning the blower.
To the OP: +1 for the P1X (though I really think you should consider the D1X if you're considering a D1SC at all).
