I change mine every 3 months whether it needs it or not. Looks as clear going out as it does going in. Dash is usually round 75%. Next change is March 4th (Wifes Birthday)

 

Direct injection soot?.....oil changes color for 2 reasons..heat and contamination.The contamination comes from water and blow by and possible raw fuel if there are any starting issues,though that itself would not color the oil, just dilute it and wash the cylinder walls down.Well, I guess if the walls were dirty it would contribute. Thats why older milage motors require more frequent oil changes( or should say the oil turns color sooner) , blowby, from worn rings and possibly even really worn exhaust valve guides( extreme).Where the fuel enters the the intake system has no effect whatsoever.Its the combustion gasses that leak past the rings that color the oil. Raw fuel getting into the oil may break down some chemicals and shorten the life but thats about it, Back in the aircraft radial eng days they pumped raw fuel into the oil to "thin" it on cold days to make cranking them easier,after they warmed up the heat evaporated the fuel.No bad effects.
Heat is another factor, but unless you have cooling problems(or a poorly designed motor) this really isn't an issue except for the turbo cars where the oil rapidly changes temps as it enters the turbo and upon shut down where it heat soaks.This produces what they call coke.Nasty stuff. Draw your own conclusions from this....

 

Yes, soot. Since you seem to have a large repertoire of knowledge, including some useful stuff, you will likely be interested in adding this: from Society of Automotive Engineers (SAE) http://www.sae.org/technical/papers/1999-01-1499 or...(just one of many discussions on the subject). http://www.wipo.int/pctdb/en/wo.jsp?...3&DISPLAY=DESC

the relevant paragraph being: "However, direct injection gasoline engines can encounter problems different from those of the conventional engines due to the direct injection of gasoline into the combustion chamber. One of these problems is related to the smoke exhausted mainly from the part of the mixture in which the gasoline is excessively rich, upon the stratified combustion. The amount of soot produced is greater than that of a conventional MPI engine, thus a greater amount of soot can enter the lubricating oil through combustion gas blow by".

 

Good answer,my apologies for not getting that memo..that was an unknown to many.....though considering how these motors are so efficient compared to the non-injected motors,there is considerably less solids( solids to mean un/partially burned fuel) to be blown by...but every particle counts. Mainly a injector fouling problem, but then we all know how a bad spray pattern will contribute to this. Funny, how one improvement causes another problem.