if you are going to do something while doing dvd compressing and then other tasks an opteron 170 or 175 are just greast deals. When overclocked your gaming will not suffer. The 4400+ or 4800+ are awesome chips too. Most people seem to fall in love with the opteron because they seem to like to take a bigger oc and the cache on opteron is higher than on the same chip from the Athlon 64 series. FX 57 is a great chip but its just plain exp and a 3700+ will overclock to the same speeds quite easily. 64 4000+ is alittle pricey for what it is and a 3700+ would do just as good.
so to narrow it down
-fx-57 - pricey for what you coudl get out of a sandy
-4000+ will get you about the same oc as a 3700, and costs more
-64 x2 4800 - great chip but with the 4400+ at 1200$ cheaper and still with the 1m cache and nice speeds gaming will be no prob
- opteron - more cache and notably higher oc's (usually) 170 or 175 will be a great bet and your gaming wont suffer
Peronallly id go with the 170 pr 175 or 4400+ all three are awesome just comes down to the price you like. GL