A quick eyeball of the global weekly sales graph shows that Nintendo is selling an average of 350k Wii systems a week, while Microsoft is selling about 130k 360s a week. The 360 has 590,000 to go to 20M, while the Wii has 1.93M to go to 30M. Dividing that...
Wii: 1930/350=5.5 weeks
360: 590/130=4.5 weeks
Of course, whereas Microsoft's sales have settled into a nice stable line on the graph, Nintendo's weekly sales line looks like it was made by a seismograph that just picked up an earthquake by comparison, so it all comes down to the timing of the Wii's supply spikes. I would say we have a 25% chance of seeing the Wii hit 30M first, a 25% chance of seeing the 360 hit 20M first, and a 50% chance that the two will reach their respective sales milestones on the same week. That's why I'm casting my vote for "same week".
Super World Cup Fighter II: Championship 2010 Edition
