Too fast and it does not pattern well and too slow does not retain enough energy. Pick your poison.
My poison is the slower load. Speed loses its speed faster than a slower velocity load does. Simple physics.
Of course, simple physics tells us that faster pellets always arrive at the target sooner and faster than slower pellets. So, all else being equal (and patterning being of all else), faster is probably better and at least as good.
I'd go with the best pattern, so long as the velocity on delivery is adequate.