Assuming that holiday sales after effect last through Jan 2009, I would guess the 360 gap will play out like this:

1st Quarter:

Jan 09 : 500K+ (about 125K gain/ week)
Feb-Mar : 200K-600K+ (Kill Zone 2 in late Feb may create a PS3 surge that temporarily narrow the sales gap for these two months. MS however, has Halo Wars, the GTA IV Episode I, and Fallout 3 expansion all coming out in this period. So the net sales gap is hard to judge).

Net 1st quarter: 700k-1100k gain for 360.

2nd Quarter:
With a $50 price drop from Sony.
Apr-Jun: 600k+ (50k gain / week)

Without a $50 price drop.
Apr-Jun: 1200k+ (100k gain /week)

with a $50 drop from Sony and MS react with a $50 drop on the pro & elite systems.
Apr-Jun: 1200k+ (100k gain/week)

Net 2nd quarter: 600k-1200k gain

3rd quarter:
Jul-Sept: 600k+ (50k gain/week)

Net 2nd quarter: 600k+ gain

4th quarter:
Another $50 price drop from Sony.
MS will also drop $50 from pro and elite systems while removing one game from the bundle. Around this time the third major revision of the 360 chipset should begin to show up. The arcade may get a small drop to $180. But MS probably don't see the need to drop the Arcade system below $199 until 2010.

With this scenario, price drops of both companies nearly cancels each other out. The net effect should be that 360 still continue to gain over PS3 but the gap will be much smaller compared to 2008 holidays.

Oct-Dec: 1200k+ (100k gain/week)

Net gain 4th quarter: 1200K+

Conclusion:
Min 360 gain in 09 : 3.1 mil
Max 360 gain in 09: 4.1 mil

Total LTD gain min: 8mil + 3.1 mil = 11.1 mil

This thread will be fun to come back to in 6-12 months.

LOL.  Yep.  I will be in trouble.

I truly believe Sony is going to step their game up this year. It seems as if this is the year Sony starts laying down the law and cracking the whip on these lazy ass developers.

Sony's Plans for 09(Educated Guess):
-Slash 50 from price early in year, another 50 fro price later in year.
-Bring Marketing up to par with Microsofts on there games and hardware.
-Release more games then ever though imaginable
-Making developers actually utilize the system's strengths such as adding trophies(if EVERY game has Achievements, they should also have Trophies.). Improvements on online experience such as HOME and the XMB in general. Utilize screen shots and in game music more!

With all this I believe it goes something like...
Minimum:5 million units
Maximum:7 million units

You can still change your prediction until the end of January.

Hmm, there are two outreaching possibilities I see, one is that the X360 continues to outsell the PS3 through the year, but rather slowly.

For that scenario the maximum gap will extend to about 11 million, and the minimum will obviously be the 8 million the year starts with.

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Another scenario sees the PS3 slowly catching the X360 in weekly sales, before outselling it weekly, and thus decreasing the gap, and then managing a good Christmas period making some decent ground on the 360.

For that I would think the maximum gap would extend from now until March/April up to about 9 million, then as the PS3 comes back the gap could diminish to as low as 6 million.

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So I guess it depends on the scenario that play out, personally I think it will be something in the middle, in that the PS3 will only start outselling the X360 later in the year, for which I see the maximum gap being about 10 million, and the minimum gap will remain the 8 million the year starts at, although the gap at the end of the year will be between 8 and 9 million.

Trust me when I tell you you will not see FF13 on 360 till 2010.

11 Max
8 Min

Max gap = 12 million
Min gap = 6 million

Maximum gap 10 million. Minimum gap 6 million.