I have one listening area of a similar shape with OB subs that work very, very well.
I am going to also take the opportunity to get on my soap box about SVS. I had 2 SB4000s paired with my Wilson speakers, and they were always "ok". I replaced them with dual RELs and I cannot overstate how much better they are. The SVS subs are closer to "it came in the package with a soundbar at Costco" than they are to the RELs. I have heard Rythmiks only a couple times, and they were closer to REL than SVS, but definitely not REL.
I would call my RELs vs my GR OB subs on-par for quality, just different in style of OB vs sealed.
Thus I would heavily encourage you towards the GR subs, and solidly assuming it will be better than your SVS. And if you find you don't like the OB style, definitely try REL.