There's really little impact having "-2" enabled even when there isn't
any phase 2 traffic. Additional processing overhead is pretty small as it only tries to
match the frame sync id.
Conversely, there is considerable benefit to reducing the sample size (-S), especially on
lower spec hardware. You only need to have it wide enough to receive one channel (57600
works well on a RPi3, 960000 and 1440000 are good on PCs). The only reason to go bigger
is to see "more stuff" on the FFT plot, but it won't make op25 perform
significantly better unless your entire trunked system fits within the 2.5Mhz RTL
bandwidth allowing you to use center tuning.