Would it be better to use a PC667 over a PC533 ram? Both are ddr2 of course..?

Answer 1

Better only if you will use the high performance ddr2 667 with low latency. Otherwise the higher latency of regular ddr2 667 would just offset its speed advantage.

Answer 2

Depends what your motherboard can support. If the bus speed on the board is 533 then getting 667 won't help. Also, are you using older memory that's 533? If so all the memory will run at 533. If the board can support it and all the memory is 667, then yes 667 would be better.