0-60 times aren't really the story (and generally rubbish as well), its the way the power is delivered.
For example, the lower gearing on the 2.5 make 2.5 and 3.0 not dramatically different 0-60 time, but drive both, and its clear the bigger engine is far more effortless to accelerate, and cruise better at higher speeds. Also, it will pull from 50-70 far better than the smaller engine.
The Omega is a big, heavy car to be pulled by a 2.2 petrol. It cruises OK, but getting it to cruise speed (esp in Auto format) needs a bit of effort. The upside is slightly better economy, and more space to work on the engine, hopefully (from an OOF point of view) giving more confidence to the owner to try more DIY work on it, and dramatically reducing servicing/repair costs.
Does rather assume that you haven't nodded off on the way to cruising speed 
Slower cars have advantages, it teaches you to get the best out of it.
A VW Toerag fancied his chances after I overtook him on the brakes into a corner, which miffed him off (he shouldn't have been going so friggin slow then), and whilst he was all over me on the straights, he was left for dust in the bends.
That, m'lord, is the reason the Zaffy's range is bum squeakingly tight.