A price drop just before GTA4 is logical, but since the launch date is totally unknown and the game keeps getting delayed over and over again I can see 2 scenarios:
1. If there still ain't no release date known by February, then MS will announce a price drop for March (because the X360 needs a price drop urgently). That might be a tiny $50 cut, but then they'll try to slay Sony when GTA4 finally arrives in ealry summer by dropping the Pro to $250.
2. Release date of GTA4 becomes more clear by February. Then a more logical lowered price for the X360 Pro would be $279 (and Arcade $199, Elite $349) a couple of weeks before the release date of GTA4 (but no later than May, because if the game gets delayed into the summer, MS will choose scenario 1).
Forget a Sony price drop in the first half of the year.