My county programmed 800Mhz radio is set to 7.8...I believe that 5.6 may lower receiver sensitivity slightly, and should only be considered if you are having interference issues with very close adjoining frequencies...in other words, 5.6 is a "fix" for a "problem", that if you are not experiencing, should not be necessary.
Similarly, unless I am mistaken, the 800MHz spectrum is still using 25Khz bandwidth for analog, even though a mixed mode system would be using 12.5 when spitting out P25. All P25 is 12.5, so setting the system to 25 would not alter that.
Paul