Hi Jack,
from the service point of view I would definitly recommend a stop in Novosibirsk UNNT. Service is great for a very quick turnaround. Did a stop with a 604 there about 2 years ago. In and out in about 20 minutes.
But for a 60 2legs of 23xxNM will be too much.
For a 2 stop planning I would suggest to refuel in Irkustk UIII and Khanty Mansiysk USHH. All legs well manageable for the 60-around 1500NM each.
Been to both Airports before I do not see any big problem with either of them.
If you consider USHH too far of the beaten path you may consider refueling in Yekaterinburg USSS.
I hope I could be of some help.
best regards
xreime