BFG's have a good softmod success rate, but it is hard to find these for under $200. I have herd the XFG's (i linked to newegg in above post) also have a better that normal sucess rate.
If the softmod fails, you can revert back to the original config easily and it will not harm your card. The softmod actually consisits of two parts:
1. Add 4 extra pipes
2. Add 6th vertex shader
so if your 16p/6VS mod fails, you still have a good chance of getting 16p/5vs or 12p/6vs to work. I would say you odds are 70% that both mods work and 90% that at leat one of the two works, and 99.99% that if both mods fail your card will work at the intended 12p/5vs that it was specked at after you reverse the softmod procedure.