The BG's generally aren't the best choice. They do have the high end deficiencies that you mentioned but they also do not have the sensitivity necessary to match the Seas line. In my opinion the Fountek NeoCD2.0 is the best choice for most La's when budget isn't the primary concern (w/in reason of course). At current prices it will run about $1800 to run 8 drivers per side (just over 50"). Rick at Selah audio has done several designs w/ these, and at least one w/ Seas woofers I believe.Check out www.selahaudio.com
Keep us updated on your project.
Good luck,
Aaron