Thanks for the info -- sticking running line on an 82' DT turns it instantly into a cheap long belly.
I'm all for cheap.
I'm after spey DTs, not so much for the length, for as you point out we'll never cast to the end of them, but for the front taper. The difference between the front of a standard DT10 and a spey DT10 makes a big difference in overall grain weight at the 60'-70' range and makes a big difference in casting weight as well (639 vs. 672 and 410 vs. 448 respectively at 65'). The standard DTs will work just fine, but because the heaviest is usually only a DT10 and often a DT9, it does limit those lines to the lighter rods.