Hi Pokey-Thanks for the reply. As to the Sierra Guide thing, I think they commissioned the book from the author Raymond Bridge. He is a seasoned cycle tourist and the author of 10 outdoor-related books. The book is a bit seasoned too, his references are to 5 and Ultra 6 speed set-ups, but his section on the drive train is in depth-35 pages.
His recommendation is:
46/42-14,17,20,24,28 for the five-speed
He likes this because the shifts are (eliminating the extreme two) as follows low to high:
6.8,4.5,4.9,5.4,4.6,15.6 (which can be spit if you want to use that last gear into 7.9 and 7.7 inches.
-the other jumps are almost perfectly spaced
-the high gear is about right for touring
-the 40 inch low is about right for a conditioned rider in the mountains.
-the first two shifts do not require a double, so no hesitation on the hills
-After that every second is a double, so easy to remember.

He sees these reasons for not going to a 3-rings:
1-the crank axle is longer
2-the chain-line is moved out, so that unless the frame is beefed up, there is more whip.
3-" The tension on the right side...between the crank axle and the rear whell axle is given increased leverage by the longer dimension."
4-The angle of the chain is greater from either chain wheel
5-The extreme combination gears are worse than in the 2 chain wheel set-up.
6-The largest chain wheel is likely to wear quickly.
7-You must use a longer and heavier chain
8-You must use a large capacity rear derailleur which is less precise in shifting, and heavier.

On the other topic though if I order new cups will I see an improvement in swaping a 125 mm free axle unit weighing 305 grams with a 110 mm sealed unit weighing 233 grams ( cups included), in terms of stiffness and Q-factor?