Either way, I doubt shield weight matters, which was the original question.
Shield speed is how fast you get it up and down from defensive stance - indirectly affecting your melee swing "speed" or more appropriate - delay.
No. only getting it up does the shield affect swing--at least according to WaltF4. Because given that he says that a one hander swings just as fast with or without a shield, then shield speed and weight does not matter.
I find this possible, but it seams to me that to confirm this our beloved WALTF4 should do some experiments with different shield weight and speeds.