Toucan, I own a BV perf but haven't put it up (yet). From what I remember, linuxman thought his perf was at least the equal of his solids, and maybe even better? He could give you the scoop on that.
I have no problem with any of the RTV S2 tps on 87W & 137W with my BV solid, and it seems like some people have issues with a couple of those tps. I haven't tried for any Ku-band with my BV prime focus yet (have with the Spoon).
8.5' is probably a little small for some of the high-FES S2 stuff, but a good BV will perform as well as a larger dish because of their surface/shape accuracy. As long as the BV perf dish has good parabolic shape and is aligned well it should be an outstanding performer.