Well the beast is finally mounted! Had to reinforce the ceiling joist to accomodate the extra weight, which involved accurate measurements, but it was worth it in the end. Picked up a 50mm desk grommet to tidy up the hole in the cavity wall for cable entry. Today will see me mount the surround back speakers (Richter Legend Rears) and some touch up paint work (around the grommet and above the projector where my dirty work glove kept rubbing off the freshly painted ceiling!). Some pics:-