I am all in favor of "buy the 16 oz. when ever possible" idea. However, if the tartan you like is only available in 13oz. AND you are unable/unwilling to pay the premium for a custom weave, I would go with the one I liked in 13 oz. before the one I liked less in 16oz. I did just that when choosing 13oz. HoE MacMillan Hunting Modern over Lochcarrron 16 oz.. I liked the colors more than I was wedded to the weight, and i was unwilling to pay the premium for a custom weave. I have not regretted that decision at all since making it.