Thank you all for the responses, The only reason I am considering the 180 is because there are a couple in the Refurb/B stock stores and the saving is significant. My original intent was three matched M5HPOW for behind the screen. Last night I checked my screens construction and the two centre supports/studs are only 36" apart , the 180 won't fit unless I rebuild the frame!

I guess the horizontal centres are really only for systems that use tall L/R fronts like the M60 or M80 then?

LCR's M5HPOW
Rears QS-10
2-Velodyne VDR12-BV
Onkyo TX-NR757
Optoma HD142x w/115" DIY AT Spandex screen