very little.
Ive got a liteon 48x24x48x which ive flashed to 52x speeds, and have done lots of burns at both speeds.
The difference in burn times is close to negligible, considering that lead in and out is the same.
48x is damn fast anyway... and its hard to find media that will do 52x all the way to the end.
The noise level is noticibly louder too, not particularly wellcome given the ah heck all difference in burn times.
so buy the 48x, and flash upgrade it to 52x later if you feel like it.
<b>My Computer is so powerful Sauron Desires it and mortal men Covet it, <i>My Precioussssssss</i></b>