Well, decision made and this is progress so far. Thanks for your help and advice Purlpower and Anne. Finally decided to go for the green Rowan Tweedy type stuff I bought from the place in Sowerby I mentioned in a previous post.
Seems to be knitting up quite quickly, the gauge is correct for the number of stitches, but about two rows more to 15cms than specified in the pattern. I don't think this will be too much of a problem.
I'm pleased with it so far, though the needles were a bit of a pain to start with. My 4.5mm DPNs are very very blunt and I had trouble with the purl three togethers and such. (I tend to start off knitting in the round by casting the required number of stitches onto one needle then knitting them off onto three, I find I'm less likely to get the knitting twisted then. I tried doing this straight onto the circular to start with and got in a horrible mess.) Once I'd got past the beginning and onto the circular it wasn't quite so bad, though even that is not as pointy as I'd like. I'm trying to keep it quite loose so that it's easier to get the needles through the stitches.
Why is it that however many needles you have you never have quite the right ones for a new project. I suspect the problem is that I've been buying cheap needles because that's what it's easy to get hold of, but I've discovered as I've progressed that I prefer certain types and I only have a few sets of those. I like bamboos as they seem to have pointier tips, but not cheap ones as they tend to drag the yarn. I'm also a bit worried that bamboos may go a bit blunter over time as they're not as hard as aluminium needles. Some alunimium ones seem to be sharper than others. I'll just have to keep an eye out and gather information as I go along.