Just re: your earlier point about 'ordinary cars' are often running with 200bhp (which I agree, it's nothing much to crow about these days) but on my way into work this morning I easily managed to get the back wheels to judder thanks - in part - to my lack of LSD, a mini roundabout, damp roads (and no-one about I might add). I've got the 'asthmatic' 2.5 V6 Auto that's as fast as a glacier with a hangover. But my point being, in terms of keeping up with modern traffic, no issue whatsoever.

I've left chavved 3series driver red faced and astonished this rusty old barge out paced him between traffic lights, kept pace with an AMG A-class that clearly thought a wallet thickness could make up for lack of driving ability, and never been beaten off the lights yet.
1.5 ton takes a bit of moving, and young Mr Fiesta ST might level-peg at first, but soon as your chav reaches for his gearchange, my 'rubbish old slushbox', still in 1st, is just reaching the top half of the rev range, and the power is really kicking in, and it's bye-bye Burberry cap. It's a smooth, seamless power(and torque) delivery with any of the V6s.
I don't want this to be read as if I'm ignoring your entire point, I'm not, just suggesting that they really are perfectly decent in every day driving, 3.0/3.2s and manuals even more so.
I do like the sound of fitting a later BMW unit, actually, certainly 'food for thought' and we know the Omega chassis handles large power increases, Monaros being the proof.