64 * 2 means 64 bit wide internal bus and dual core procesor. This means it has two processors on one chip that work together, and they will each go a lot faster than a 32 bit wide processor, plus the machine wil run more applications in the future that are designed for 64 bits.
I assume you get about twice the speed you would have got with a single core clocking at the same speed. Apparently, dual core are good for multitasking also. This is what I would put my money on.
The size of the memory only effects the computer speed when you start to run out and go into disk cach, which uses the hard disk as memory. Most new machines seem to offer 1 GByte of RAM anyway which is plenty.
Regards, Kyri from sunny Cyprus