Rel Strata III versus Rel Britannia B3

I can't answer about either one of those subs, but I would like to suggest that you listen to a Von Schweikert VR/S-1. I have used this sub with the Spendor S5e's, and it is a killer. Very fast, and when set up right it will blend in with that speaker as if it was made for it.
I now have the Spendor S8e's, and guess what... I am still using it with these beautiful music makers that go down clean to about 30Hz. I use the lowest crossover point and it adds just the right stuff to complete these very musical full range speakers.
I love this sub! When you take the time, as you should with any sub, and you don't crank it up too loud... blend it with the main speakers... this sub will hide out and add depth and a very solid bottom end.
I use the Audio Research VSi55 integrated tube amp. It has a sub RCA output, and nicely controls the sub output. Use a good interconnect, and a good power cable... that puts the whip cream on the cake!
Try it... you might like it!

I have heard of the B1 (500watts) at a dealer showroom. I cant describe the magnificent bass that box can produce. It really locks into the music, very fast , seamless, very solid. I cant describe it in words but I definitely want to have one!

Thanks for the recommendation on the Von Schweikert VR/S-1! I will see if I can find one to listen to. I juct picked up a B-3 on ebay for $1200 and will let you guys know how it sounds. It might be too much sub for the room, but we'll see.

Anyone out there with Strata experience?

Thanks!