Ideally none of the routes should have to live with the Darts but there you go. If it was me I would probably take the Pulsar off the 12, and maybe shove a Dart on Richmonds too to help spread the pain around. If I had to guess I would say the Prestiges are not suitable for the X66 as I bet they keep overheating. 4007 used to be close to boiling on the 21A4001 wasn't brilliant on the X66 last week when I rode it, was glad to be off.
Never seen a Pulsar on the 12/12A yet, normally you end up with a Dart or Prestige on the 2 or 11 instead.
Anyway, 7484 is on the 81.