LO I think it's fair to say APA et al don't have access to the F35/F22/F15/F16/F anything or SU anything performance models. I think the US is a bit more unique in that repect as they have had access in the past to several MIG models and some Sukhoi's and clearly know the performance envelopes of their own kit.
I can't imagine any modeling of the PAK-FA or others would be anything other than guess work though.