You might want to place a call to the engineers at Banks in CA. I have bought things from them in the past and they have generally been good about telling customers what various moves done would do to a truck and how the sensors, etc. are affected. I have been less then impressed with the information provided by some fairly big named aftermarket tuners about this. It seems pulling the DPF really allows them to use a heavy fueling tuner on these trucks but I am not really sure if anyone knows whether it would affect the engine long term. One concern I would have is whether removing the DPF without recalibrating the engine management system would affect some of the sensor reads and thusly the performance long term. I trust Banks the most because they have taken the time to invest in the highest grade equipment for testing and actually have the finances to BUY test mules, rather than using volunteer trucks for test beds. I am sure they have pulled DPF's off trucks in testing and would have some data about its affects, whether modified or not. My impression is that taking the DPF off sounds like a bad idea. One thing you might do first if you have not already is make sure your 6.4L has the most updated operations program. My 6.4L did not, as I purchased it mid model year in 2008. I took it to the dealer and was getting 15 mpg unloaded on highway and about 9 pulling. After the recalibration, I was up to 17.5 unloaded and 12 pulling in the same driving cycle--without potentially harming my warranty. I will say that I am a bit of a gearhead and have had my diesels modified over the years almost without exception, either for more speed or for more economy or both. Now, with these trucks having so much performance from the factory, coupled with enhanced drivability also, I have stopped seeing the point. I know of folks who have removed their DPF's on practically new trucks and have honestly wondered why. If I were to consider this route, I would probably discuss it with a trusted source such as the one above first. Good luck.
John M