Don't get me wrong, you should indeed put the car up at £6k and see what you can get, its a very clean motor and looks worth that kind of money any day. Valuations vary in the trade press and obviously prices are not so strong as they were, but its not unreasonable even so.
Dealers are sometimes asking more than top book for cars yet some others price at the mean line average to turn the cars over. Private pricing is somewhat different so go for it.
I know that most folks would probably take the tdi version as the sensible option nowadays anyway, and it will be a selling point to the right crowd, the ones likely to be able to afford the car.
If it was pimped out and rolling with 19's, big turbo conversion etc then it would attract the kind of guys who couldn't buy it anyway (tyre kickers and test pilots lol) so you are in the best spot there I think.
If its spotless, straight priced at £6000 and running sweet, it will sell itself with the right wording in the ad and good pics. Use the autotrader since it gets very good coverage, and also start a 7-day, 1p "wheelnut" auction on ebay to generate interest and free advertising.....