The Cisco ASA appliance is supposed to at some point replace the PIX, but from what I understand the highest end ASA is not quite on par with the PIX 535. I am not sure if they will come out with a higher end ASA appliance or not. The only reason I know this is because a friend of mine's company run 2 535's and their cisco tech talked to them about the fact that the ASA would be replacing the PIX and it would be enough for what they were doing with them, which they could probably get by with a 515.