Redeemed there's nothing wrong with your 5770. [H]ard compared one to the new GTS 450.
I know you can't afford it, and if I were spending my own cash on a bang for the buck card today, it would be the GTX 460. I'd grab one and shoot for 850 on the core with Afterburner. The MSI Cyclone card can likely OC to that level and stay around 61C load. At least techPowerUp! was able to do that with one.
For folks that can spend 225usd on a GPU, go with that and manually OC it. You won't be sorry.
If they bother with the rebate, it's 205usd.
BTW if you want extra push from your 5770 try OCing with the same tool, MSI's Afterburner.