+1 for the dual PC13-Ultra OR the dual Rythmik FV15HP
Honestly, no "wrong" choice there at all! If you like the looks of the Rythmiks better, that's as good a reason as any to go with them.
I do love the SVS Ultra subs. On a purely subjective level, I go a little gaga over that freaking beautiful driver

I love the linearity too and its insanely low distortion. I also just love the Sledge 1000 amp for all its features and immaculate power delivery. But it's also a smaller driver - it has to work harder and accept more amp power to equal the displacement of the bigger 15" in the Rythmik. And as the measurements show, other than at 20Hz, the Rythmik can actually pump out a bit more output thanks to that driver size advantage.
Get the subs that fit best with the rest of your setup. You won't be disappointed with either! If the Rythmiks' cabinet design and looks work better for you, go for them!
