David, 4.8's with manual boxes are very very scarce. Having said that though, I have always been a manual-gearbox man, but the 4.8's tiptronic 5-speed box is seriously awesome.
As to which of the two is better: the 4.8, without a shadow of a doubt. Except that it is also a hell of a lot more complex, and thus could potentially give you more gray hairs.
The 4.5 is a lot slower than the 4.8, but it's honest and dependable, and the less money you spent on it, the less it hurts dragging it through the brush.
So what I am saying is, we can't tell you which one to get, you have to figure out what's more impoertant to you.
Mag ons ons kenniskry met lekkerkry aanhoukry.