the other thing to keep in mind is that depending on the complexity of the plaid (mine is very simple with reds an browns) you can pleat how you like. So, 4 yds might do, if you have small enough pleats (and that works with the stripe or sett). I like deep pleats, and am fairly wide, so, I wear between 7 and 9 yds of 52" or 60".

Give it a shot and see how it works. That is one of the lovely things about great kilts. There really aren't any wrong ways to do it.