If you want stiff/light/comfortable all in the same bike, check out the KTM Revelator range. Again in the STW fashion if recommending your own bike, I’ve been running one for a few months now and it is a very impressive frame. For £2k off the shelf you’re looking at full Ultegra, Mavic Ksyriums and a Fizik saddle too, so value is good. Weight wise it’s a 7.5kg bike, which is good for that money. I bought a frame and built it up with a selection of my own components, running a mix of SRAM Force/Red 10spd, Hope Pro3 SP/Stans wheels and tubeless 25 Schwalbe One’s, mine comes in at 7.5kg including pedals, cages, Garmin mount and cadence sensor.
In the world of internet bargains right now though, I’d struggle to look past the 2013 Cannondale Supersix Evo with SRAM Red at £2099 from Paul’s Cycles. A massive 40% off! Amazing frame, the best/lightest 10spd groupset out there (11 really doesn’t add anything IMO, except more expensive and faster wearing chains), and for a bargain price. Only thing I’d do to it is sell the Ksyriums and go tubeless on it.