I've not really been impressed with any modern RELs, not since the 90s anyway. Things changed when they were taken over.
The SB2000 is an excellent performer though, particularly for its size. I've been extremely impressed with mine (in a 12'x14' room, roughly), and I've been even more impressed by its effortlessness and overall output in our demo room, which is much larger at about 5m x 5m.
Going by the specs, you'd be going from a 8" driver with a 200w amp in the REL to a 12" driver with a 500w amp in the SVS. The T7 also uses a 10" passive radiator to shift more air (boost the output), but I personally have never been keen on passive radiators used in subwoofers - yes, it gives you more bass, but you're relying on that driver reacting to the air pressure within the cabinet, and that's where 'speed' comes into question. The quality of the driver and outright amplifier power contribute to bass depth and output.
Try it though. If you have a nearby dealer with one on demo, get a loan and try it in your own system against your REL. Unless something particularly good comes along, I'm tempted to add another, although the SB2000 has all the output I would ever need for the room it is in.