The base spec boardman Air 9.0TT is £2k with sram rival and Aksiums is no where close to the spec of the £2K Planet X DuraAce, Cabon crank & 101/82 carbon wheels.
The only real advantage mere-mortals can see is the boardman has internal cable routing & BB30 bottom bracket.
I doubt many people would be able to see a real difference in stiffness the bb30 gives and the deep section wheels would outweigh the internal cable routing aero benifit of the boardman.
For me the planet X is the best value tt bike out there, is not the most exotic and good look finding it amogst the other 50 in transition but their popularity speeks volumes
The boardman Air 9.4 looks lovley though but 2X the price for a similar top groupset and own brand carbon wheels
my 2 cents anyway
Nath