I posted a rather heavy box of magazines to New York on 1 February using Royal Mail's 'International Economy' [Surface Mail].
My buyer has just messaged me that she received her parcel today - 8 days later !
I can only assume it went Airmail, as Surface Mail is usually 3-6 weeks for the US.
I have another packet of magazines to send tomorrow, again by 'International Economy' - wonder how long this one will take?