I'm still contemplating the new vs vintage tradeoffs. Is the newer 1861 (on a new speedmaster) any more reliable or better than the older 861s? Or vice versa?

 

I don't believe there is any significant difference between those two calibers. A few tweaks, no more. There's some good info in this thread ...

http://omegaforums.net/threads/speedmaster-calibers-321-vs-861-vs-1861.6563/