I must say that if you work with Matlab everyday, it is really frustrated with Mathematica in some points.
Find is one of the most frequently used functions in Matlab.
Find(array>5.0): returns indices of the elements that are greater than 5.0.
In Mathematica, the corresponding function is Position
Position[array, #>5.0&] or Position[array, _>5.0] just doesn't work.
We "simple-minded" Matlab user have seldom thought about putting constraints on patterns
Then, this will do the job
Position[array, x : _ /; x > 5.0]
Position[array, x:_ /; testfunc[x]] will do better.