Ok so looking at this from an analytical approach:
| Current | +10% | +20% | +30% | +40% | +50% | +60% | +70% | +80% | +90% | +100% |
360 | 17 | 16 | 14 | 13 | 12 | 12 | 11 | 10 | 10 | 9 | 9 |
Wii | 21 | 20 | 18 | 17 | 15 | 14 | 14 | 13 | 12 | 12 | 11 |
Each square lists how long each console will take to pass the mark at a given sales rate (measured in weeks, rounding up obviously). Obviously the first column is the current rate and each subsequent colum represents an increase in sales as stated.
Squares in Red are "Cannot Win", Orange squares are "Likely to Lose", Yellow squares are "Likely to Win" and green squares are "Cannot Lose" (assuming no console exceeds 100% increase to their average, which is as close to a sure thing as you can get).
In short, I think the 360 will get there first, and I think I make a damn good case for why.