My Elite also has a tendency to wander around a bit. Its done it on Michelins , 452's and 912's, all felt exactly the same. I dont get this problem on either my VW Golf or my TVR wich also have 452's on.
I did have a severe tramlining problem for a while which turned out to be geometry fixed by WIM 
What tyre size and pressures you running on the omega?
Standard size tyres 235/45 17 at 32psi. Havent tried experimenting with the pressures on the 912's as my tyre guage has broken....
Thanks for coming back with info.
A bit concerning to me as i started with exact same psi and the size is the same.
I have issues and you dont.
I do have issues , the Omega wanders around a bit and needs regular small steering corrections (but its not so bad that its a real concern). Its not the falkens as it did it with the michelins too. I had theboy turn down the power assitance on the steering which has improved it a bit. New front wishbones and new rear springs havent made any difference. Steering idler, box etc all checked and fine so not sure whats next to try. Might go for a new donut bush on the diff , its possible the rear is a bit loose and that could be causing it.
Yes, your no the exact same path i was on, did all the usual fixes and ran out of things to try once the donut bushes where fitted,(i assume that what you mean) the originals had a creak and failed the mot. Fitted senator donuts from first line and could feel the difference/improvement and the creak has gone, but the wandering is still there. If it aint the tyres... Well, dont know what it could be...?
Like you though, i think i had become used to some pulling no the steering wheel and when the back started to move around i assumed the donut bushes would cure it. But no. Then i drove Kevins car and realised how bad my car was and how much i was putting up with. Road work seems and groves just did not affect his at all. You could feel the bumps and the suspension ride them but no pulling no the wheel at all. My car however was a mare over the exact same route, i didnt realise how bad until i drove Kevins.
There is a width restriction in Reading i have to go through now and then, the tarmac has dipped where all the cars have been though leaving 2 tram lines. My car pulls like mad through there, the
s.wheel as almost at 3 oclock position just to keep it straight and not hit the curb. Its like the tyres are trying to clime out of the trench, if you know what i mean...? Not nice.