Arryn,
yup, I agree that speed of expansion is not THAT important in SP, but since I try to play my SP games in order to prepare for MP I am fairly focused on speed (most likely since I feel that I am lacking in this department
).
Especially with R'lyeh (due to its fairly weak initial units) I imagine that it will be fairly hard to be competetive in MP without choosing a SC as a pretender.
I haven't played enough of the other races to be sure about this, but I think the magically strong races need time to get their power up and when they are jumped early in MP are going to be defeated, but they are getting stronger the longer the game Lasts.
The heavy hiting races on the other hand are very strong at first, but their power will not get up as fast. This should be an initial advantage in MP.
This might force the magic heavy races to make some very risky decisions which can break them early on or enable them to survive till midgame, where they can start to shine.
CharonJr