Hi,
The fairly simple answer (simple? what does that mean) is that you will play best with whatever you feel comfortable with.
Height alone does not dictate what will feel comfortable.
Im 6 foot 2 but my irons are only +.1/4inch, a friend is 5'10 and is +.1/2inch.
Other things influence this also. Do you stand upright or stooped? do your arms hang down or out a little at address? Do you allow the club to lie flat on ground or toe up/down!
I think the most important thing is to make sure the length of the club shaft allows your hands to be right distance from the ball to allow sole of club to lie flat on the floor and the best way to find this out is to be custom fitted. That way both shaft lenght and clubhead lie will be as near as possible to your correct spec.
If custom fitting is not an option then comfort and checking that iron hits ground with middle of sole and not toe up/down when swung are most important factors.
Haha if all that fails and your still unsure, go with longer shaft as you'll hit it about half a club further!!!!