I'm thinking about replacing my SVS with something with a bit more punch.
No. I haven't heard your SVS though. I have always enjoyed REL auditions with music (dealers probably just knew how to implement them, as they are always found at high end establishments), but IMO they simply don't cut it for HT, at least not for the money. Granted, I'm pretty spoiled. In that line, I've heard both the 305 and 505. With 505, I had LOTR fellowship cranked, with BW 804 mains, and 805 surrounds. The sub was the weak link.
The problem could be if you are only looking at sealed subs, outside of perhaps JL Audio. Their Fathom series are actually pretty similar to REL 505 pricing, IIRC. Now, there, just no comparison.
For the money, you will want ported for HT.