Actually, from what I've read of Martin's vision, even the 15th century was a bit advanced for him. 13th and 14th centuries were closer to what he imagined. My view is not to focus on any period, I personally love the high renaissance, particularly italian armor. I wanted to show advanced armour on the lords in my artwork, but use older forms for the various lesser lords and knights and hodge podge of styles for the men at arms. This would reflect a more fluent use of armour, not fixed to any period.