Thanks for that, I knew that circular milling technique had a proper name, but my google-fu wasn't strong enough to find it!
Just had a quick search over on the CamBam forum, and it can apparently do itm so I'll go and do some reading and try it out.

I had a first attempt today, and it went pretty well. A continual gentle stream of air, combined with the odd squirt of WD40 kept things running well using the 5mm cutter to do the main roughing profile pass using a pretty conservative DOC. I never got to the 4mm stage, as I screwed up the toolpath generation meaning it bypassed spiralling a couple key holes in the centre, so I never let it go any further.