Report: warm-warm selection on Frigidaire 2140
I ran a load of cottons this afternoon on Warm-Warm setting in my Frigidaire 2140. This model does not have Auto Temp Control, so Hot = hot water line only, Warm = both hot and cold water lines used, Cold = cold water line only. I used Normal cycle with Extra Rinse enabled, so that there were three rinses in all. By touching the intake taps/hoses, it's easy to tell which lines are filling the washer on the rinses.
Results:
Rinse #1: COLD
Rinse #2: COLD
Rinse #3: WARM
So on this machine, at least, the Warm rinse comes last and does not prevent cold water being used for the first rinse and, if selected, the extra rinse.
However, on this machine, the clothes are spun only gently, not at high speed, while the rinse water is being drained. So if we accept the "rubber backed mat/rug" theory as being correct (rubber less likely to crack or flake if warm when spun at higher speeds), this strategy would hold true in my washer, since the high speed spin at the end would occur with the clothes warmed by the last (warm) rinse. However, if it's important not to have temp changes for wool, as Laundress suggested (and she's almost always right), it doesn't say much for my washer's ability to avoid fiber damage when switching from warm wash to cold rinse. Of course, one has the option of using Cold-Cold for wool, but what everyone I know seems to say is that you use warm-warm for woolens because the soap rinses out better. Who knows?