There both 3.0ghz with 1mb of L2, but the FX 74 is a socket F 1207 and the X2 6400 is a Socket AM2
So, your answer is?
Zangetsu
If you are building a new computer then why not get E6750 or Q6600 ?? Both perform better and overclock better. E6750 is about $70 cheaper than 6400+ on newegg