What difference does the bit make? Do you even know how/what that effects? The 5770 is faster then the GTS250, even though it has "only" a 128bit bus. (the 7600GT is about as fast as the 6800GT, even though it had a 128bit bus for the same reasons.)
Your computer looks a little off. You have a 6core CPU indicating a need for a scalable CPU. (meaning encoding work) Most people don't pair this CPU with a GTS250 unless they want to play games. If this is mostly a game playing computer dump the 1055T and get the 955 or 965. Your encoding will be a bit slower, but your gaming will be a bit faster. I'd actually suggest getting the i5 750 for a better gaming experience.