The 4650 will outperform the 3450. One is a low profile card (4650) the other is standard (3450) if you need a low profile card, get the 4650. If you don't need a low profile card get a standard size 4650.
You can check the entire article for pricing recommendations. However your 250w power supply will not supply the needs of ANY gaming card, so you'd also have to replace your power supply to play the games you listed.