Just thought I'd post back and thank everyone for their advice, as of today I'm a proud 5D Mk II owner
. I haven't had a chance to take any especially interesting shots but gave it a test under varying conditions and I can't find much difference in the center focus point speed / low-light perfomance versus a 7D. As some commented the outer spread of focus points is not great (well pretty bad), and I tried to repeat a shot I'd taken recently through a bird cage using spot focus that it couldn't match, but I expected as much.
Now for the good part is that banging on a tripod and taking a few food shots the colour reproduction was fantastic. Outside during the day the FF gave my 70-200 a much better focal range and shallow depth of field for the style of photos I often take. Got some nice shots at night too using a 50/1.4, I expected a nice ISO boost but it seems to handle dramatic changes in contrast much better too. I'm a happy camper and look forward to giving it a good run over Christmas. It will really complement my 7D well rather than replace it
About my biggest gripe so far is the location and type of power switch, I saw a post recently by someone asking about how to extend the standby time. I didn't reply but thought why can't you just turn it on & off between shots but now see where he was coming from. I put mine of a tripod earlier and just about needed a screwdriver to get at the switch