listen mate i dont know if its worth it at 27 with a mortagage to pay but you only live once and knowone can say for how long or how the latter parts of your life will be, the years go quicker as you get older there isnt really that much time to spend.
one things for sure, get that fast great sounding car nxt as diesel,electric cars are coming and petrol is only going to go up, our only hope is bioethonol less economy but 20% more power, easy to make the government will make loads on that (102ron) so we might be in luck.
but with pay per mile charging you may aswell go out with a bang, consider the next 5yrs of uk motoring the twilight period, you can always sell later on.
get a GTA ... ohh and put a autodelta quad pipe system on and carbon fiber intake, perhaps later on a ferrari throttle bodie (they sell them for the gta not too bad prices)