It's very simple, really. We've taken four of the most recent sub-£40k family performance cars, and put them on a track to find out which one would win a half-mile drag race. Because that's what you do with your super-saloon when it's not on the school run, isn't it?Our first competitor is the 400bhp Vauxhall VXR8. The blunt instrument of the pack, and the hardest to get off the line, but will brute force win in the end?The Audi S5 can't be left out. With the much-praised 4.2-litre V8 from the RS4, four-wheel drive and 349bhp, we reckon this one will be hard to beat, though weight may be an issue.Joining the Audi to defend German precision engineering is the BMW 335d Sport Touring. It may be an estate, and it may be an oil-burner, but don't discount the BMW - torque counts as much as power.We can't have a drag race without the latest competitor from Japan, so the Subaru Impreza RB320 joins the line-up. On paper this is the fastest car of the group, doing 0-60mph in 4.8 seconds and with a top speed of 158mph. Whether those numbers will translate to the track is less certain.And finally, because it will soon be no longer and we love an underdog here at Autocar, the Jaguar S-Type R. Rear-wheel drive, 400bhp and plenty of weighty luxury accessories, this is how to do the half-mile in style and comfort. But will it do it quickly?Click here to watch the video and find out which of our worthy competitors crossed the line first.