Personally for me the Medusae are all about the visor. I think the GW model is ok but I don't like the brain thingy, too space squid for me. I'd rather have more sinister looking models.
I did a bit of research and found that the guy who makes these models is a one-man-band garage operator who sculpts them in limited runs, selling hem where he can. It looks like he's got access to some proper casting forges now and is looking at selling more of his range. I found these on his blog:
I think I'll email the guy because these would be perfect for Medusae for me. Stick some hands on them and chain them up and you have some sinister looking models.