I realised i never fully answered your question. No issues with GPS at all (give it a minute or so to find them, after that rock solid). Elevation data is, I think, barometric (alongside GPS data); meaning much more accurate that GPS-data-only devices. The XL gives me gradient info (which it derives from your forward movement, so there is a slight lag) which is great (if useless) info on long climbs. The landscape screen orientation is fantastic: massive and clear numbers. As far as I know colour screens cannot (yet) match mono screens for clarity in sunlight (not that it bothers me, very happy with just black+white). The Mega XL also allows you to invert the black and white, so black screen with 'white' numbers (to go with that black bike ... ).
