You're right Sy - £8k get's a very hot saloon right now.
A used S6 would steal the show for me, particularly as an all rounder. I've always like that shape and would love a V8. At just £8,000 in today's money, it must get a lot of people thinking... Me included!
Even being a tender 24yo, insurance wouldn't be an issue I don't think, nor would tax or the price of the car as such. I think the regularity of visits to Shell and servicing it would hit the wallet hardest.