Great, thank you. So worth getting carbon over aluminium alloy frame but not to worry about the shifters too much!
Generally these things go with the budget, with some crossover.
You won't find a carbon bike with Sora, or an aluminium one with Dura-Ace (doubtless someone will come along and prove me wrong).
There might be a bit of cross over, for a given budget you'll either get a carbon frame or next groupset up.
I'd say choose a good shop, set your budget, stick to it (always tempting for a bit of an upgrade) then see what they recommend/what the options are at that price point. £2k will get a great bike, and whether there is relatively more of that money in frame or shifters won't make a great deal of difference!
As I say, though, others may have different opinions.