Thanks guys and sorry for the delay in replying to you both. Good point about import settings. That exercise was really just about playing with PS but if I can get split toning to work the way I want it to in LR, that saves a LOT of effort.
Another bit of experimentation today - how can I shoot with flash in midday sun without HSS?
ND filters! This isn't great by any stretch, but as an experiment to further my knowledge it's been useful. I mounted a decent-sized diffuser onto a solid light stand above my "model" which helped lower the direct sun down to a gentler fill. I stuck an ND4 (2 stop) in front of my lens which at f4 was reading 1/250, so just in range of sync. I put my Smartflash on 1/4 power firing through a beauty dish and this is the result:

Experiment with midday flash by
Paul M, on Flickr
And perhaps a more successful one of her brother:

Silly face #3741 by
Paul M, on Flickr