I'd swap the Astra VXR for an Astra 888.
Very nearly the same performance, but with 40+mpg. Still does 150, just you can't see anything behined you for the soot. 1.9tdi engine.
New exhaust, another remap, panel filter say hello to 350lb ft torque and 220bhp ish.
Comes with 4 pots etc as well.
Or, i want an Audi RS4

Sod fuel costs, let that engine rev, dribble. M3 V8 is for city ponces who want the badge