I've solved my problem. As I said earlier, I've used Porta NC and loved its pastel colours. The problem was I always found it a nightmare to scan as I could never quite get the hang of correcting the orange film base consistently so I got 'faithful' colours.
I know APUG isn't the place to discuss this in detail, but I can wholeheartedly recommend ColorNeg, a Photoshop plug-in that allows scanning faithful to the original negative film colour:
Now that I've got this fixed, I'll keep using Portra 160 NC rather than looking for a tranny film with a similar look...!