Yes, a heavy armor can slow you down, though I doubt anybody has ever noticed this slowdown unless they put on a heavy armor and a heavy shield and then walked around without vigor(which every hammerdin needs to max anyway).
A Goldskin is a Full Plate Mail. And a Full Plate Mail slows you down more then a Ornate, kinda odd that.

An alternative would be a heavenly garb, it has 10 res all, 15 energy, 25% regenerate mana, 216 defence and it's light, meaning no slowdown and only 41 str needed to wear. Combined with Iratha's full set makes for a very effective hammerdin. This will also allow you to keep your str near base, though Iratha's helm requires 55 str, you could resolve that with some str rings. Iratha's also gives 20frw on top of whatever your boots give.