I've just been reading the September 2010 edition of the Rock garden (Vol 78 number 3). On page 341 is a picture of Arenaria melandryformis from Tim Lever's (et al) trip to Bhutan. The (closed) flowers don't look like your picture but the leaves do so I wondered if it was actually an Arenaria rather than a Saxifrage? The Arenaria in Tim's picture has pronounced and attractive coronas behind the flowers, rather like Sax bergenioides - did your plant have this feature as well Philip? Your proposed ID suggests it may have done even if the picture does not show it.