[Phew, I'm glad THAT little exchange vanished! Scary. 'Nuff sed.]
"BTW we have a new iMac as well (and dislike it massively at times! Anyone recommend a decent file manager and photo viewer?)."
For an OSX file manager I don't think you can get better than Cocoatech's Path Finder -
Path Finder 7 by Cocoatech - It is not cheap, but is incredibly powerful and versatile as well as being easy to use.
For simple image sorting and minor adjustments, XnViewMP -
XnView Software · XnViewMP - is free for home use, and works nicely.
Pixelmator is not expensive and
"delivers Photoshop-class tools for a fraction of the price, including powerful, pixel-accurate selection tools, top-notch painting, drawing, and retouching options, more than 160 effects, and an elegant collection of professional-grade color correction tools."
The oddly named GIMP (free) -
GIMP - The GNU Image Manipulation Program - is the big cross-platform gorilla of image manipulation programs. On a level with full-on Photoshop in terms of it's capabilities, it's originally quirky GUI has gotten much better and you can do absolutely anything.
Finally, LemkeSoft's GraphicConverter -
Lemke Software: Image Editing, Slideshow, Browser, Batch Conversion, Metadata and more on your Mac - is an odd hybrid of photo-manipulation and management software. It costs, but I use it a lot, 'cos it can do some useful things very fast and well that my other image apps can't.
Best of luck!
Mac
PS: Thanks terrain safe - I guess I should have another look at the Surface Pro 3