have you considered power2max campy? cheaper than SRM. Around the same price level as Quarq for higher end models, but with more model compatibility. if you're buying a stages WITH the right crankarm the power2max will not be much more expensive. http://www.power2max.de/europe/en/Produ ... peed-road/
why you would not be convinced with Quarq and powertap but convinced with Stages? Quarq and powertap have been around a long long time and customer service with both have been good. Stages support may be difficult depending on where you are. and there is the disadvantage of left only power. it's not much of a disadvantage, but it still is one.
I'll admit I have no experience with power2max, ( I use a quarq) but I was seriously considering one and only went with quarq because of a good deal. if you're in europe or the US I'd go power2max . I'd only heard good things about them so far.