I would not worry about MP
I would worry more about getting 8 million or 10 million GOOD pixels

Canon announced the 1DmkIII with some XTi features, mainly the less dust generating materials, dust removal in DPP Raw software, and anti-dust shake system in front of the sensor.
Also the user controls are more 20D like, which I'm very happy about.
Improved auto focus.

And a £2999 price tag last time I looked online.


So for a solution the main bane of my life (dust) I'd go for the XTi