i have decided that i have to find the problem with my omega, i refuse to be beat, So first would i be right to remove the cat, cut it off and weld a straight piece of pipe in its place, before going down the Ecu and wiring route, I say this because i have had a few people tell me that the symptoms are that of a blocked cat, This would be the cheapest option to start with i think, what does everyone else think. 
That's the spirit.

I'm no expert on exhaust stuff, but if you can remove the cat reversibly, rather than destructively, that would probably be better. It could just as easily be a clogged up backbox, so you don't want to destroy the cat only to find it makes no difference.
I'd imagine there must be
something electrical wrong, in order for it to have run badly enough, for long enough, to block up exhaust parts (if that is indeed the 'main' problem just now).
Have you paperclipped it at all?
http://www.omegaowners.com/forum/YaBB.pl?num=1189022687