For 2015 the average across the country was 32.5% for wind. [1] Texas appears to be several percentage points above the average, and newer plants often are better than old plants (if they have similar sites).
Here is state data from 2011-2012 [2], with a handy map [3]. It looks like Scurry County might be in a good part of Texas. In principle, the data for 2015 is available here [4], although one would have to process it.
We are seeing capacity factors well over 45% in Panhandle now. ERCOT rated the various windy areas of the state back in 2006. Scurry Co. was 10th or 14th if I remember correctly. Not as high cap fac as Amarillo and other areas north of Lubbock. But CREZ Panhandle is already constrained due to the nature of putting lines in the middle of nowhere with no load and no inertia. Scurry Co is on the other side of the constraint, so good move on Amazon's part. Great location with respect to wind resource and transmission access and deliverability.
Not sure of the exact figures, but whether or not the wind farm is in a constrained area or not generally determines if they can generate full out or if they will be capped at a lower level to keep from overloading the transmission grid.
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