I'm no expert, but I have read that the 32x speed increase is not really that big of a boost. The 40x, I've heard, is pretty awesome, burning a cd in under 2 minutes.
The 24x for $50 is probably better. You can upgrade later to a 40x when they run a special at OM, OD for, say, $60 AR & AC.
Just my 2 cents...