ok Paul, from the hip
Forget the car you have seen. You won't "miss it" It is almost certainly expensive from the OPC. I would not recommend buying from an OPC unless buying new (I wish.....997 Turbo please).
That car is extremely common, there will be loads and loads of them exactly the same, but some might have a lower price, better service history, some added extras you like etc, so you have a choice. Even after a few weeks of looking and you still think the garage and finance and car are the ones you have seen already, I would almost guarantee the same car will still be on the forecourt - not much is selling at the moment. Even if it's not, another identical car will be along the following week.
There are loads of specialist Porsche centres that deal only in used Porsche and cost a lot less and servicing can be less than half the labour rate per hour. Look one up on Google or ask on one of the Porsche forums like
http://www.porscheclubgbforum.com/default.asp easy to register for free and ask all the questions you need to, plenty of other porsche forums
Don't touch the finance deal with a barge pole. Go on one of the comparison sites and get a loan if you need one or add to your mortgage at cheap rates.
You're worrying about the wrong thing if you are thinking about petrol costs. You can get late 20's if driven well. Depends what you want the car for. I don't often drive it fast, I love the look and feel of the car and use the tiptronic most of the time. If I want a blast, switch to manual and we're off
No point is buying a 'dream car' if you don't get that sinking feeling in your stomach every time you look at it or drive it, so take you time and get the right one, there's no rush, but please forget the one you have seen, waste of money and better ones out there no doubt.
As for Boxter, I hear all the arguements and agree it has a bit of an image problem, but with the roof down, gun metal grey colour, 'S' version (don't buy the non 'S'), it's a lovely car to look at and drive.......but you'll pull up next to a 911 and go "oh boolocks - wish I'd spent a couple of quid extra and gone for the daddy"
WeeJohnyB