Thanks for the replies guys!
I am enquiring because somewhere near where I live is looking to install a system and they are undecided as to which way to go with this!
They would like to go for a digital desk and the Presonus Studiolive 24:4:2, Soundcraft Si 24 and possibly Yamaha LS9 are options. Recently I saw the Allen and Heath iLive desk and noticed that this uses CAT5 and looks to be an impressive desk but am unsure if it is worth the £5000-£8000 price difference?
There is no real comparison between the iLive and those consoles, the iLive blows them out of the water IMO.
The A&H GLD series digital console, which also uses Cat5 for a digital snake, is much closer to the consoles you mention. I am looking to get a demo of the GLD here in the next couple of weeks I hope for two different systems, but thus far from what I know of it I would take the GLD over any of those consoles as well.