I think a lot of it depends on your driving style. Some people love that the diesel gives lots of torque low down, others hate the fact that it runs out of puff at medium revs. Maybe figure out which is your preference and decide that way.
What I would say is that if you do prefer petrol and you've got a lot of driving to do, maybe you should consider for an ordinary 2.2 rather than an S. The ride will be much comfier and I'd be surprised if you couldn't force a decent deal out of the salesman in the current climate.
A decent remap will get you 12-14 bhp on its own, but if you replace the induction and/or cat back exhaust, you can get a lot more (20-30). Not 40bhp though, they must have meant 14!!
Also consider other running costs - 2.4 will munch front tyres quicker than 2.2, and they're not cheap! Balance that with higher mpgs from diesel but also higher purchase price and diesel prices to work out what's better for you over the likely length of your ownership. I've got a feeling there's not much in it. Personally I'm actually better off in a petrol as my mileage is too low to benefit from diesel mpg savings.
Brat Pack no.8