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@gbj_tester
I actually did calculations, assuming acceleration from a standing start to 33mph in 15s, the extra 200g robs you of 1.5W, out of 750W required for accelerating you and the rest of your bike and about 600W of aerodynamic drag at the maximum speed. Working back to distance covered in the time with the acceleration reduced to account for the extra mass puts you about 25cm behind after one lap.
Other things which are in the >1W gain range:
Changing from a very good tyre to the best one
Changing from a very good aero helmet to the best one
Changing from a very good pursuit bar to the best one
Moving your elbow rests by 5mm from where you are to where you should be
etc. etc.
If you're in the accumulation of small gains game, the choice between Campag and SRAM cranks needs to take account of bearing drag and aerodynamics as well as weight and stiffness, because they are all going to be in the same order of magnitude. You need to measure on a full system, since bendy BB axles cause chain misalignment, so you need to measure transmission losses too. It's not even enough to measure the mechanical losses, since crank twisting causes the pedals to be canted under load, which likely has a physiological impact on the rider's ability to exert maximum power. If you don't have the resources to measure all these factors under full load full speed conditions to a resolution of 0.1W, you might as well go with aesthetics since they are both good.