No they are around the same size, the main difference is that the door on the OVX is deeper and more square than the OVX. But the basic shape and size is about the same. The top housing on the OVX is smaller than the OVS's top housing, so that makes the OVS only a wee smaller I think, (I have an OVS and like three OVX's) but they are about the same size.
Hmm, ok, but the latch is different on the OVS, which is a push in latch to open the door for relamping, and I believe the OVX has a pull latch to open the door for relamping. Correct me if I'm wrong. But I do believe that.
The OVS has a latch style that is more... More like the old westinghouse ones but not quite, it's smaller, has two little slots and is a little bigger, the older OVX has a smaller latch, one slot instead of two, and it's smaller, the new OVX latch was longer but still the same, so it was easier to get off, and the latches from OVX, OVZ, OVH are all the same, and when they changed the hinge style they changed the latch style on all three models.
The latch is not different. The OVS has the same basic latch Cooper and Westinghouse have used since the late 70s. Cooper changed it from two catches to one catch around 1990 or so (but the latch looks exactly the same when the light is closed) and they made the latch longer in the mid-2000s like Ian said, to make opening the light easier. It's pretty hard to open their lights while wearing lineman's gloves, especially the OVX and OVH, with the smaller latch.