When it comes down to performance comparison between the 965 and the 975 chipset the 965 has the reputation for higher FSB speeds upwards toward 600 and ignores the 1066 and 1333 straps.
The 975 is also great for overclocking but hit a wall earlier than the 965.
The higher multipliers found in the E6600, 6700, and X6800 are just more favorable to overclock without crazy FSB speeds and high Vcore .
Both chipsets are great for overclocking and very dependable.
In most cases it’s just a mater of preference along with a little luck.
Or are we talking about Avatars ?