For US - UK trips the surcharge in PE is $475 and Business is $1025 one way , so a $550 fee would be about right
For UK originating trips to the US, the difference is about $366 one way

It is great that AA doesn't impose the surcharges on redemption upgrades on itself, but BA sucks on the teat of surcharges and wants every last drop it can get

As mentioned , there would be no difference in taxes since the standard rate of APD will have already been paid