OK, slight change of plan. Due to a ****-up on the ordering front with the iron wire, I ended up with some wire which is a bit too thin (0.5mm inner diameter) as they specified the outer diameter on the ordering page, rather than the conductor diameter.
On reflection of course, that makes perfect sense since this isn't wire for electrical purposes at all, what use is the 'conductor' diameter?
Wire with an external diameter of 1.8mm's on its way, which I hope will have ~1.2mm diameter conductor.
So, in the meantime I've been experimenting with wire I have been able to get hold of, which is shiny steel. It turns out that only 30 paces from my home is a hardware store which sells it - so I've tried winding chokes with it, just to see what happens. I've also acquired an LCR meter to see what kinds of values I'm getting at different measuring frequencies.
The first pair of chokes I wound with some really thick stuff - 2.8mm. Having aimed for 20 turns...