In reply to Antigua:
> I'll be honest I'm not a bike expert and don't understand what your saying.
> I have a budget of about £3.5k.
> I originality thought that I'd get a Specialised Tarmac Expert Di2 which had been reduced from 4 to 3k that would allow me to spend the £600 to upgrade the wheels to the AC Aero 420's
I have a budget of £3-3.5k, with the emphasis on £3k. Having looked at a few "off the peg" bikes I could get for that money (Wilier, De Rosa, etc), I would end up with a bike with a lower groupset than I wanted and cheap wheels. Attempting to build to spec through LBS would blow the budget and I'd still end up with cheap wheels.
So, I'm building it myself. Sourcing the parts separately (and mostly in sales), I will be able to put together nearly £5k of bike for just over £3k and some time. Warranty shouldn't be an issue, as each part has it's own warranty.