A bit of an update; firstly that you all for your input and advice it was most welcome.
Yesterday I went to test drive two Caymans, one being the 2.5T Cayman S with PDK and the second being the GTS 4.0 NA with a manual transmission.
Cayman S 2.5T to GTS 4.0 NA comparison:
I drove the GTS first and followed the dealer in the 2.5T on a B road 'Porsche approved route' , I must say that I was very surprised on how well the 2.5T went, for me to keep pace I had to be in the right gear otherwise he would pull away! Although, on the occasions I did pre-empt his his right foot I was right on his tail but only marginally gaining albeit I did have a passenger and he was on his own. I think the take away from that for me was they are both very capable and in real world conditions very little in it although perhaps the 2.5T matched with that PDK being a bit more flexible in terms of delivery.
Back to the GTS, I really loved the drive, smooth linear power delivery, and that manual gearbox was just sublime a real a joy and something I have missed in my M240i. Even though perhaps it doesn't have the low down grunt of the 2.5T it still pulled very well from low revs and never felt lack lustered at all. The icing on the cake for me was the 6 pot sound behind your ear, what a great sound! Amazing!
When it was time to jump into the 2.5T I immediately noticed the extra low down shove from the turbo, but when flat out it never felt quicker than the NA even with the PDK, I had a bit of a play with the paddle shift but after a few minutes I just found myself laying back and letting the car do the work for me, I just get lazy in autos!

The last thing which was noticeable was the 2.5T could not match the throttle response of the GTS which was instant and confidence inspiring especially when exiting a corner, the 2.5T may just be a little less forgiving with the way it delivers it power.
In the end and for me I preferred the GTS and 4.0 manual over the 2.5T PDK, although I think the PDK in the NA would take it up another notch those shifts are lightning! I did come away with more respect for those 4 pots that I originally had they are fantastic engines that really go! incredible!
I put in an order for a GTS and expect to take delivery some time next year, this is going to be a long 6 months! [

] I went a bit more on the specification than I had ordinally planned and ended up with the following:
GTS 4.0 MT in Agate Grey Metallic.
[ul][*]GTS interior package Carmine Red[*]‘PORSCHE’ logo painted in Satin Black[*]20-inch 718 Sport wheels painted in satin black[*]LED main headlights including Porsche Dynamic Light System Plus (PDLS Plus)[*]Light design package[*]Electrically folding exterior mirrors including courtesy lighting[*]Automatically dimming mirrors with integrated rain sensor[*]Cruise control[*]GTS interior package[*]Heated multifunction steering wheel[*]Sports seats Plus (2-way, electric)[*]Two-zone automatic climate control[*]Smoking package[*]Passenger footwell storage net[*]BOSE® Surround Sound System[*]PPF protection package by Topaz. [/ul]Once I get a date for delivery I'll join up and become a fully fledged member, being a bit geeky if anyone knows of any good books explaining Porsche engine development including the 4 Pot 2.5T and new 4.0 NA engine then please point me.