Tom Kirkman, I had wondered how single foot and double foot guides effected action of fly blank. I have read that double foot guides do stiffen rod blank, but I wondered if combined weight of epoxy, thread, and eyelet overcame rod blank stiffening in the 1" rod blank area a double foot guide would occupy.

Another point not mentioned is weight created by each ferrule? Sure, 4pcs rods are the norm, and preferred for travel. Do ferrule's stiffen or soften rod action? A 2pc rod has 1 ferrule, a 4pc 3, a 6pc 5 ferrules, what is net effect of more vs less ferrules when it comes to rod action? A few rod manufactures are making One piece fly rods!

For me, a one piece fly rod would be a tip breaking nightmare!! But, in the spirit of keeping weight savings, and rod true to designed power and action, this must be as close a design as possible?

They don't affect the action at all (action is where the blank initially flexes). They do slow the speed of the blank (reaction and recovery time). This is why it becomes softer, not stiffer.

If you take the stiffest guides you can find and wrap them end to end along a rod blank, you'll find that you have a wimpy noodle of a rod. It'll be plenty soft. Weight is the culprit - the rod blank has to carry whatever you add to it.

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If you build any bamboo fly rod, any fiberglass fly rod, or a graphite rod with anything but an extra-fast action you will be wasting your time agonizing over saving tiny fractions of an ounce in the guide train, for you have already settled upon a slower rod .

Thanks to everyone for all the replies. I think my question was answered quite adequately. I know questions I didn't ask were answered quite adequately, and the information, as usual, was more than welcome. Essentially, I like the aesthetics of the single foot guide, but was concerned that there might be a limit to line weight for rods on which they were employed. Apparently, a five weight works. I'm no Ed Jaworowski, so I am unsure that the advantages of weight or speed would have any impact on my casting. It is what it is, and has been for decades. Fortunately, it is not an impediment to catching fish. Again, thanks to all.
Slainte,
Hunter

From ghoulies and ghosties,
and long leggedy beasties,
and things that go bump in the night,
Good Lord deliver us!

Another advantage I think with the single foots (at least with the Minima's that Tom mentioned), is the ability to use a running guide as a tip. They are lighter than even a wire tip top. And this reduction in weight is at the most critical place on the rod. Use a good locking wrap and it's not coming off.
Those who care about aesthetics will probably squirm a bit. But, sacrificing performance for aesthetics? No reason.