FSB freq of E6300 is 266 MHz. So the minimum RAM speed you need is DDR2-533, but new RAM slower than DDR2-800, or maybe DDR2-667 is hard to find.
I suggest the fourth one (DDR2-800 CL5). It is a little quicker at the same price.
Although the RAM is faster than you need, the motherboard will set the operating speed of the RAM.