Well, after struggling for a few hours with 100-200k connection (seriiously, it was that bad!), I've now installed the Netgear WGT624 (V3) and she's flying:
19mb downloads
1.6mb a second .... I can live with that!
The wireless option is pants, still won't reach my kitchen/dining room which is only 20 feet away. Still, that's why I'll never get rid of my Devolo homeplugs. They're the best bits of IT kit I've ever bought.
Thanks everyone for your help!