Hi Maserati Man,
I am going through exactly the same dilemma. Having listened to the knowledgeable people on this forum, it is a very hard call. The GTS (a real one, many are not) is the best model. I like you am torn between the best of the last Duo Select cars, and a good 57/08 ZF car.
The GTS you have seen has been around for a long time, yet is low miles and a cheap price. There is another GTS for sale near Beaconsfield (one of the regulars posted a link on another QP buying thread) This one is the same colour, with a black interior but with the suede/alcantara inserts. Hopefully the regular will post a link.
By the way Ewan's GTS is amazing, the best colour, and best interior, and looked after to the n'th degree.
Happy hunting