Ok, all the answers are on the forum but I'll help you out!
Standard trim has cloth, GT has leather. That's the biggest tell tale.
All UK cars had gold brembos.
The early cars (orange strip down the light) had 276 bhp. In 2006 it got 296 (different headlights) and in 2007 came the 309 bhp model. It has a bonnet bulge and two air intakes under the bonnet.
The TC is switchable.
There is a trip computer.
That is the absolute basics. Have a search about and you should find all the differences and buying guides etc. You can also post up links of cars you've seen and people on here will confirm the model etc.
When getting into imports it gets complicated!