To be honest I don't think they'll drop much at all. After all, its not a major leap in technology to the Ti versions, and I doubt the older ones are just going to fall into sellers laps. I would be surprised if you save more than 30-50dollarpounds by getting an older one.
The Ti's got more enhanced vertex and pixel shaders.
The stock speed of a gf3 is 200/460 anyway, or at least that's what I've been led to believe so far - and what mine was when I bought it.