Thanks Andrew
your screen shot was helpful, but unfortunately with my version there was no GPU at the bottom. Turned out I have the latest version for Mac(9.1.1 I think). However I went into photoshop and found GPU but the changes did not help. I am still at a loss, but truly, thanks for the effort. Any other ideas??
Martin.
PS I have a MBP also running the same versions so will try to compare.