Wouldn't normally ask but

Really looking for ST advice. I have a 09 Specialized Transition Expert upgraded with Easton Attack aerobars, Dura Ace 7900, Rotor 3d crank w/ qrings, HED3c front wheels and Zipp disc. I have $800 to puts towards something else and not a penny more. I have a giro advantage 2 and race suit. Some things I was thinking of were…

Quarq (although would probably get rid of Rotor crankset and sell it)
Giro Selector
Powertap

Not sure what the best way to go is. I could get a Quarq sell the Rotor set up and have extra money for helmet and something else. Wondering if Quarq is the way to go and maybe just switch between bikes? Not sure and would like some input. Thanks

from the choices given…

powerpowerpowerpowerpower

and either the time to learn how to use it on your own, or the $ to find a coach to do it for you

quarq.