AA miles for BA Upgrade?
 

I'm gonna assume that one cannot upgrade on BA with AA miles (trans-atlantic). Does anyone know different?

yes you are right. You cannot use AA miles to upgrade. You must use AA miles for the full ticket.

however you can use AA miles to pay for a b-class ticket on BA

My understanding is that the transatlantic segment is still on AA with the continuation on BA if you book a BA award from AA.

Can you use AA FF miles for award travel on a BA flight from Tampa to London?

AA has always told me that you have to fly across the pond on American. We will fly AA to London on ff miles, then transfer to BA for our flight to Marseille.