u dropped the downpipe /cat to see if it is blocked - mine had a p0300 on a blocked precat
it is rare for the ecu's to fail on these engines, coil packs do fail but are quite rare
fuel pressure problems were on the vectra C, the high pressure fuel pumps would show no sign of failure but your car would fail to start or run properly
if no ecu codes are showing then u might have to look at mechical side, ie compression, timing is out, blocked exhaust
if she runs oki at idle then u plant it then starts to misfire then it could be a blocked cat cos the exhaust fumes are not being pushed out quick enough and it is pressurising, drop the downpipe, only 3 bolts and start her up, it will be loud but see if u can replicate the fault