Hiya!
Thanks for the comments so far.
I should have added, I'm on the latest version of Mountain Lion & I don't have Photoshop. Primarily I use Aperture (often with a Nik plugin or a VSCO preset as a starting point), along with the Perfect Resize Pro plugin (I also use Capture One for initial RAW processing, or Vuescan when needed). Thus resizing and sharpening in Photoshop are not a consideration.
I don't really want to use Parallels, Fusion, etc., so this also precludes QImage - which I found when I was mainly Windows based to be a fantastic programme. Really wish it was also made for Mac, but alas, seems it never will be.
When I feel the image is ready for printing, I make a new version and resize this with Perfect Resize (I don't resize in increments, but for larger than A4 I might look into this, so thanks "orbancc" - it's something I 'knew but forgot'). Once happy with that, I make another version and sharpen this for printing with Sharpener Pro (Nik plugin).
My main concern was that, once opened in Resize Pro, the 'embiggened' image shows up with odd sizes and resolutions displayed at the bottom right edge of the image in the preview. For example, I recall an image that should have been 170mm on the short side (basically a 2cm border for A4 paper) @ 360 dpi was showing as something like 52 inches @ some oddball resolution. I'm worried that if the app thinks this, then the values it applies for the "inkjet, paper type, viewing distance and nozzle resolution" setting might not be optimal.
On the bright size, the last couple of days the image has been showing up as the correct resized values. Just not the resolution. Also, the prints do seem fine.
Thanks.
Dean