low n stiff/hard so it dosnt have as much body roll when side ways 
lol i dont want sports fwd cars
Ok, don't want to be picky but coil overs aren't for omega. Not in the true sense of the word anyway. Reason being the rear has a totally seperate shock from spring set up. So a coil over spring (coilover) is not applicable there.
Nor is it appropriate on the front. Omega has McPherson strut front suspension. It might seem a minor point, but this involves an offset spring v shock alignment where the spring centre line is aimed directly at the bottom steering knuckle/ball joint on the wishbone. Where as the shock is angled differently within the spring and points in board for various reasons. A traditional coil over spring set up does not allow for this.
To be more helpful, we need to understand the set up v ride height issues that will affect tyre wear. If its lowered too far, the camber angles start to wear tyres massively to the point the adjustment required is not possible without fitting camber adjustment bushes at the rear, beyond 20mm lowering. Front is more forgiving.
15mm lower than standard = omega Mv6 lowed sports chassis. Gm parts only. Pm Andyc on here for tc prices.
Beyond that it starts at 30mm drop and aftermarket parts and tyre wear becomes an issue so camber needs to be carefully checked that its within spec on the rear. And be aware that fully loading the car will put the camber out of spec. causing inner edge wear.
30mm drop. Beware rear ride height(try to stay within 20mm drop)
Springs, Irmscher are considered best but very difficult to find. Eibach, Stienmetz being slightly softer than Irmscher but still plenty firm enough to stop excess roll.
Shocks.
Gm oe shocks for mv6 lowered sports chassis will take 30mm drop, but no more. Andyc.
Bilstein b4 will also take 30mm drop without issue.
Balance motor sport stroke eibach, Bilstein etc. or just google for prices.
IMO...
Irmscher springs and bilstein b4 shocks give an excellent Balance of firmness to avoid roll, but still compliant enough to give comfortable ride. 30mm drop but with the rear raised back up 10mm to keep the rear camber in spec. By placing an extra pad under the rear springs.
Hope helps.
Avoid coil overs.
