Thinking about a getting a Powertap led to this question (my road bike is 700c and Tri bike is 650c).
I’m sure this has been on this forum before but I do not recall seeing it.
If you can achieve your desired / optimum fit on a tri bike utilizing a 700c wheelset, what are pro and cons to actual performance for 650c vs 700c wheelset?
Thanx
I’ve had this conundrum before, and that is why I now have a 700 tri bike…now I can PT full time.
If I were still in your shoes…I’d get the PT in 650…you can do all of your off/early season training by PE. In fact the offseason is a good time to leave all the meters and monitors at home and just listen to your body for a while…you might find a long lost friend. 
…the powermeter is most useful when you start doing targeted, race specific work as well as during the races themselves.
650c has a lower moment of inertia, important really only on steep climbs. Typically has lower mass, but now most “superlight” wheels only come 700c. I’m not aware of any 650c wheelsets under 980 grams, but there are several 700c wheelsets you can buy now, so mass is no longer a real advantage.
700c wheels have more tire options and those tires offered in both sizes have less rolling resistance in the 700c size than that of the 650c size.
650c wheels have really been kept around as a fitting tool as aerodynamics, weight, and acceleration advantages have left the 650c behind.
SRM, Ergamo, and Polar wattage devices get around the wheel size limitations as well as drivetrain, and race wheel differences.
-SD