I been hear for a while - i use a Pentium D (More or less a el cheapo dual core) - the only thing that wont run on more then one core is BSP, because the windows IO library that i use for BSP culling is only designed for one core.
The x64, are optimized for AMD 64 - they might not work as well with Intel - i also don't own any 64 bit CPU's - so if your having issues, fall back to the 3.4 Final build that uses SSE1