X5WOMBLE - I just bought myself a nice pair of polarised Ray Bans and have exactly the same problem. Mine's a 2002 X5 with an upgraded Mk IV unit like yourself. However, as pkhines points out, if you sit in the left seat the screen perfectly clear, but obviously here in the UK we're not gonna go very far sat over on that side.

I guess the solution is a screen upgrade, or simply wear a pair of non-polarised shades - shame! Had I not bought them in the USA I'd take them back and exchange them.