I see this decision is still occupying your mind. 🙂
I have a soft spot for Velodyne as stated here (along with other suggestions):
http://www.whathifi.com/forum/home-cinema/is-the-velodyne-spl-1200-ultra-a-good-match-with-tannoy-signature-revolution-dc6t
I heard the previous series (SPL 800R/1000R/1200R), which shouldn't be far away and the incremental improvement should be the same.
The 800R was the best small sub I'd ever heard, until the Paradigm Seismic 110 arrived.
IMO. There was a noticeable step up to the 1000, but when I compared it with the 1200R, I thought the difference was worth the extra, in a room 14' x 22' x 11' (I think it was around £200 more).
I see you own the 1000 ultra, and I'm not sure it would be worth the hit to change, especially as the Ultra series is a good bit more expensive. This is just my opinion, so you would have to hear the difference for yourself and see if the cost to change is worth the extra performance you will get.
my room is slightly bigger than the above, I was looking at the SPL1000 but see the 1200 goes that bit lower in its frequency range. I am willing to pay that bit more for deeper tones, will this be noticable from the 10" driver up to the 12" ?
One of our customers recently swapped out his SVS cylinder for a GXW15, saying that while it didn't go as low, it did more of what he wanted from a sub. Maybe that was down to it's sealed cabinet or it's on board EQ, we don't know, but that was his choice after demoing the GXW15 at home directly against the SVS. I haven't heard the Velo, so I can't comment there.