Well... thanks for all input ...i sized up a 54 in a shop today to confirm everything and its now bought. Ta. Will post back to let all know what I think once built up and riding it next week. Ta again.

 All built up.... fantastic bike... have a 13cm stem running at the moment cos of the doric seatpost being straight through and not having much fore-aft adjustment possibility, its running further forward on the rails than I want... this is only a stopgap cos I have the stem now anyway. Got a 20mm layback post sat here (Deda Superzero) will be dropping that in and changing for the 12cm stem any minute which is defintely going to be right as predicted. Thanks to all for help with decision making, really happy now.

 I'm confused by your measurements. i have an 87 inseam and sternal notch height of 149.2 and same length arms but I'm shorter than you at 178.1. This must mean you have a long neck and/or a tall head. I ride a 56 because the drop, with my leg length, on a 54 is too great.