I don't have the SPM, I've got the Red Dawn, which is either a step up or down, can't remember. At the time I bought them, I think the Red Dawn were the top of the line.
The one great thing about flatline cables is that they're flat. Beyond that, I couldn't hazard a guess at whether I'm really noticing any sonic benefits, or I just bought into hype.
I'd a/b them with something solidly constructed, but cheap. I'd be interested in your conclusions. Yes, by the way, mine are bi-wired, and I don't know whether that adds or subtracts or does nothing at all.