I dont think the pro is worth it. I just went with the standard. For the extra $100 you get the cadence sensor(the virtual cadence on the standard works just fine 99% of the time), the customizable display (standard display is fine, cur/avg/max power + torque on top, cur/avg/max speed in middle, dist/time/cad/cadavg/work/odo/hr/hravg on bottom), and a clock.
The clock is the one feature of the pro that I would really like to have on my standard, it has an internal clock... you just cant access it while riding.