Hey Truckee Jim:
It's nice to see how the CC test confirms some suspicions and throws some preconceived notions out the window, eh. As for the 6 wts needing 35- 37 feet of line, that sounds about right for a Sage. As Bruce Richards points out, most rod companies "sort of" rate their rods based on a typical cast with approximately 40 feet of the rated line outside the rod tip. So, your 6 wt needing 35- 37 feet of 6 wt line to load properly is consistent with that.
As far as the shorter rod becoming less powerful is concerened, most rods have the stiffest sections in their tip ( to avoid collapse during casting) and in their butt. Removal of a section of the tip may well reduce the overall power of a rod with such a blank design. Chopping off a couple of foot of butt will also reduce the power of a rod. Some folks turn 5 piece rods into 4 piece lighter weight rods. It's a neat way to get a custom rod.
As for your final question, check out www.superbob.org
. This site lists the CC numbers for many of the blanks on the market today. While there is going to be some variability as a function of production process variables, the numbers listed here will help you narrow down the choices to a select few blanks. Then, all you need to do is CC the blank before wrapping it, just to make sure it is close enough to meet your needs.
Sounds like you need a few more 6 wts, anyway.....