I've been using GST a lot recently and certainly no hint of it being particuarly inaccurate to any noticable degree upon arrival from FL90. Of course, height could be a factor as MF bands are subject to some refraction and reflection and the closer you are to the surface the more affected you will be by these effects where they occur.
Apart from that there is just the usual issues of being within the DOC (25nm for GST and OX I think), wings level, etc.