I think that 60-30-10 split is unlikely as it would require 10,500-3,200-1,900=5,400 NA deliveries in December (
see InsideEv Monthly Plug-in Sales Scorecard). Given Tesla's indication to Credit Suisse that current production rate is 1200 car/week this would require that all 100% of the production capacity be dedicated to NA for 4.5 weeks straight, which IMO is an unlikely scenario. With the assumed split of 55-35-10, the required December NA deliveries would be 17,000x.55-1,900-3,200=4,250. This could be achieved on average with about 88% of the production being allocated for building NA cars for 4 weeks.
The 55-35-10 split is the latest we heard from Tesla, in the beginning of this year, if I recall correctly.
Regarding the prioritization of NA, the reason is that Tesla guided to deliver in Q4 about 2,000 cars more than to be produced. This is not possible without working for NA deliveries almost exclusively mid-November through mid-December.
----Update-----
I think that main takeaway from this kind-of-joggling-of-numbers speculation is that in case Tesla meets the guidance, as they seem to have indicated to Credit Suisse, there will be seriously eye-popping record deliveries in December in both NA and Europe.