I read the post (http://www.audio-illumination.org/forums/index.php?act=ST&f=15&t=3381) wherein poorimpulsecontrol showed identifiable attributes of different --alt-preset settings.

What caught my eye was that extreme and fast extreme were identical except extreme uses vbr-old / vbr-rh while fast extreme uses vbr-mtrh. Correct me if I'm wrong, but isn't the latter mode a newer and better way of encoding vbr? If so why does extreme use the old method?

As you said, this is the situation :

extreme => vbr-old
fast extreme => vbr-mtrh

vbr-mtrh is the newer algorithm(?) for encoding vbr files, it's supposedly faster than vbr-old but it's quality is a tad lower than that of vbr-old.

So my suggestion is, if you're in a hurry use vbr-mtrh otherwise use vbr-old because you'll encode your files once but listen to them many thimes.

BTW : nice signature you have there

I was unaware that vbr-mtrh was a tad lower quality than that of vbr-old. I thought it was the prefered vbr mode for quality as well as speed.