I am building a 9 ft. 6 wt. Epic fly rod -- the 690G. The blank is a mere 1.34 ounces, or 38 grams, so super light for a 6wt.

I am wondering how much the weight of the reel seat will matter? I have a Struble real seat that weighs 21 grams, and an American Tackle real seat that weighs 28 grams, and another that weighs only 18 grams. I am not sure what the typical real seat for a 6 wt. rod weighs or should weigh.

This rod will be used for trout fishing in mid to larger western rivers such as the Eagle and Gunnison in Colorado, the Madison, Big Hole or Bitterroot in Montana, etc.

How concerned should I be about real seat weight? And from others experience, what is the average weight of a reel seat for a 6 wt rod?

Because of where that weight is, small differences such as you list are not terribly important. It's the weight further out near the middle and tip area of the rod that you feel and which impact performance.

..............

And how much does yore reel weigh??
You're concerned with grams - the reel will eclipse the seat. Just choose the seat you want.
Herb

Yeah, if my reel is 5 ounces, that's 142 grams, so I guess 5 extra grams of real seat weight will not amount to much.