It seems these days that spares on the Sixes are almost as common as branded Versas. I would've sent the Two's Volvos to the Sixes, and the R1 Versas to the Two, since the Two is a flatter and more urban route. It would leave the Sixes with quality vehicles for a good long time, and the Two to potentially get new MMCs in the future.
I also had an idea, that the 6.1 and Transpeak merge into a half hourly route from Derby-Buxton via Belper, Wirksworth, Matlock and Bakewell, leaving these places with an altogether better trentbarton 'Transpeak' with more heavyweight vehicles and the shorter Ripley runs stay as the Sixes which the Versas can probably cope with better.
I know that's about as likely as pigs flying, but I can dream.