You'd be better off getting a regular Brisbane. There aren't any 65nm opterons so despite the fact that you'd be getting more cache and usually higher grade processors, it's still not worth it for the 90nm technology + the price you're paying.
Get a brisbane - 3600 X2s are very cheap. VERY cheap.
If you're looking, just make sure you get the ones with the odd GHz; i.e. 1.9GHz, 2.1GHz, 2.3GHz, etc., although I think they also have 2.6 and 3.0. Just be careful you're not buying older generation stuff.