you would need a newer CPU for that. they are both 10 years old now and things have changed.
look here your dual core against the pentium g3258 dual core.
http://cpu.userbenchmark.com/Compare/Intel-Pentium-G3258-vs-Intel-Core2-Duo-E8400/2434vs2720
and that is a difference of 7 years
this is this generations dual core now with hyperthreading
http://cpu.userbenchmark.com/Compare/Intel-Pentium-G4560-vs-Intel-Core2-Duo-E8400/3892vs2720
I'm afraid your throwing good money away on such an old platform
my system is similar to yours, 955 black and hd 7950, both old AF but I forgot trying to replace just the CPU long ago, when for the same price I can upgrade to a g4560 or g4600