Cheers, OzEx, old chap.
Yes, the 1000ft clearance comes from PANSOPS (where its called Minimum Obstacle Clearance) and so you'd expect to see that worldwide - as you know, of course.
But nothing seems to tell us which distance off track to take in. I even wonder if an operator is free to make up his own formula (obviously with the agreement of his local Regulator). Its actually something we're considering doing as none of the methods offered in JAROPS quite suits us...