has anyone any experience of using the hasselblad 250 sa lens with a digitial back?, i'd be interested in the results, thanks!

Yes, I have used the 250sa with various digital backs (Kodak, Phase, Hasselblad, Leaf, and Sinar). As you would expect, the aberration correction (no CA) and color quality is quite high. However, I do not have a direct comparison with the less expensive non-sa version of this lens, so all I can say is that the sa version will not disappoint. My only problem with it is the rather long close focusing distance, which is why I prefer the 300TPP. The 300TPP focuses much closer for tight portrait work. The 300TPP carries quite a high price tag, but people often forget that you are really buying two extremely fast lenses, a 300/2.8 and a 500/4.8, since the 1.7X extender is matched extremely well (similar to Leica module). One advantage of the 250sa is that it has a leaf shutter, and so it can be used with higher flash sync and can also be used with the Hasselblad Flexbody.