If you frequently drive short trips my guess is your going to have carbon build up problems. Original poster claimed his commute is less than 10 minutes each way. Short trips are the worst thing you can do to an engine. Engine runs rich, low EGT's oil probably doesn't even reach half its operating temp. The oil suffers from fuel dilution, doesn't get hot enough to burn it off. The oils additive pack is beaten up and its flash point greatly decreased. Then throw in the pcv operating under a vacuum condition dumping your condensed water/fuel laden oil vapor directly into your intake manifold and you get oil caked to your intake valves. That kind of schedule should have an OCI of 3K max miles. All direct injected engines suffer somewhat from fuel dilution as they never truly run in lean burn mode like their european counter parts due to our less then steller fuel quality, beaten oil additive pack, to long on OCI and you get carbon. So fuel is likely an indirect cause of carbon build up. Longer drives will certainly stretch your oil change interval though.
Since my Supra Turbo days i've been an Irving gas fan boy, its just noticeably better then Shell, Mobil etc. Its so much better that I can tell when my wife gets lazy and fills me up with shell. I have read, I believe on Bobistheoilguy that Irving is as close as a european fuel that you can get, its Canadian, so it must be good right? haha. I concur. My car gets at least 2mpg better then shell running irving. Means it runs leaner with a hotter burn, so less carbon. I also don't suffer from fuel dilution in my sump. My Supra pulled so much less timing with Irving 93 then it did with Shell 93 that it was laughable. Problem is you can only get Irving in the NorthEast. Its the only fuel I'll put into my cars.