It should be enough. I had a 5" screen counting the frame on my 40b for some Red Eye Tree frogs and it was perfect. The bottom of the tank stayed a bit more humid, but it gave the Reds basically 2 zones they could be in depending on what they wanted.

If you think you need more ventaltion you could always drill some holes in the top of the vertical tank and either install something to frame a screen or silicone window screen over the holes.