Thanks for the replies.
Unfortunately I don't have certified air data nor the actual aircraft's POH or what ever the equivalent is for heavy metal.
Just out of interest I dug out my copy of"Handling the Big Jets" by D.P.Davies. He suggests steady state (presumably that component along the runway although not clarified) upto 15kts as protection against windshear; with half the gust component upto max 5kt additive. Total additives not to exceed 20+ unless "exceptional conditions". Not sure if Mr. Davies qualify's as barside banter.
Surely with all the flight tesing that is done; all of the accumulated low level weather data; the cost of building runways; the critical flight phase; and the seriousness in under/overestimating approach speed that aeronautical engineers have known the answer to the question "What Approach speed?" for years!
TIM