I found an Executioner with audio masking and upgraded it to G5. Slightly regret not waiting as I have unlocked Yarden but neither of the two engineers who offer scopes so cannot add a scope yet. After the upgrading, I found a G3 with a scope. RNG laughs at us. But I am about 3 mats and 4 covert theft/heist missions (tried for the first time yesterday, 2 out of 3 ain't bad) short of unlocking scopes.
Having used the Exe with audio masking a number of times, additional mods are nice but not essential. So, after audio masking my choice would be a scope and stability (to get that second round off quicker). If pushed to add a fourth mod, probably mag size. Due to the slowness of the rounds, greater range is a bit problematic as the target has to be stood still for several seconds up to 100m. Adding another 50m to the effective range though just adds to the time of flight.
Main thing to I noticed with audio masking, is that the targets need to be isolated when shot at, else their companions will notice the target falling. It also seems that no one, not even the target, notice when rounds miss!
Steve 07