Plans usually tend to get changed as time goes by, true PC2-5400 will work perfectly well @ 1:1, but it's basically the same price as PC2-6400 (800MHz) and you can 1:1 a 3.6GHz O/C out of the e8400 without extra cooling or VCore changes (or extremely small one).
But, if you are 300% sure you'll never try to OC, then the 10$ you'll save on a 2GB kit can be put elsewhere I guess.