Well after much deliberation, I've taken the plunge and bought a Brother 3034d!
Having spent ages reading about it and also thanks to the replies on here, I'd eventually managed to narrow it down to similar models made by Brother, Elna, Bernina and Janome, then found that there's a Brother dealer close to me and also there was an ex-demo 3034d for sale, with blind hem foot and instructional DVD included, for £209. It looks pristine and still has the full 3 year warranty, so I've gone for it.
In an unexpected turn of events, rather than be bored to death by my incessant talk about overlockers/sewing machines/sewing in general, my boyfriend has actually started showing a real interest in it! He likes the idea of being able to make his own cycling kit as the good quality stuff seems to cost a lot of money for what it is. I couldn't ever have imagined him being interested in sewing, but perhaps there's hope for turning him yet!