Accuracy is not a function of RAM and CPU cores available. That's speed.
Of course, with more power, you could potentially get more accuracy in the same time by running more iterations, but as far as I know, practically all operations in orbiter are solved analytically, which means that again you couldn't sqeeze out more accuracy.
Somebody lately did a pretty thourough test of the accuracy of the orbiter physics engine, and concluded that it was pretty damn accurate. Can't find the thread right now, though.