Take this:
Sapphire 9800 (blank designation, non-SE) 'Atlantis' 128mb: ~$140

You'll be able to over cloak the CPU/Memory to a 9800 Pro and maybe XT without problem. 9800 performances are better that a 9600 XT.

Take 128MB. The 256MB is just marketing and doesn't really help in game except the latest game.