It could also be the cap is doing a better job of smoothing ripple and the sensors see the less noisy supply as being at a lower overall voltage.
Or that it has more reserve so it gives a more stable supply, lower at low loads, but higher at high loads and you're measuring it at low load....
There are too many factors in the design of the supply and sensors to be able to tell without getting a full circuit diagram and knowledge of how the sensing is being done.
If it's less stable at the same speeds than it used to be then it could really be a lower voltage, but if it is as stable or more with high loads on, then it's just doing a better job.
My advice: Ignore the actual voltage reading compared to the old one and perform OC'ing, temp measuring and stability testing the usual way. It's likely to be giving you more voltage stability and less ripple than the old cap.
