Is your SVS 3000 a sealed enclosure or ported?
I have two S/510. They have more than enough output for accurate music reproduction, but they aren't quite enough for loud explosions, etc for home theatre. I use a third SVS 12" ported sub for that. The REL S Series is really more about accuracy than output volume.
I've never tried to crank the S/510 beyond what's needed for accuracy. I would imagine that with the right type of music and cranked up, they would get pretty loud.