Steel beams, plastering and acoustics

Heavier plaster - maybe 13 mm fire on resilient channels would make the most difference. Can't imagine any problem with the steel. The main problems with noise tends to be lack of detail at junctions - eg, insulation needs to go over top plates, fire rated sealant (much heavier than std) to seal gaps. I'd consider getting the plasterboard to a nice consistant 10mm gap all the way round, then caulk that with an acoustic sealant like fire caulk, then set the corners however you'd like.

really think hard about all openings, so pay attention to electrical cable connections for lights - ie try and avoid downlights

Great - does Fire Caulk have acoustic properties, because if so it would make better sense (I think) than finishing the brickwork to beam joint than mortar. I don't see how you'd use Fire Caulk around the board edges, except to fill a gap that was corniced over - You couldn't use it with a flush finish, as there is little gap to fill, or with shadowline, where the gap is maybe 15mm ... or am I missing something?
Cheers

Yes it does, and your first feeling is exactly what I was thinking - to be corniced over . Sheets close as possible to the corner, seal the gap, then cornice over

http://www.hbfuller.com.au/products/...272256631.html

Looks like the go, thanks. I think it may be better to use this to seal the gap between the brickwork and I beam than builders mud also.
Cheers