I agree that the UMP-45 is most effective using burst/full auto with a supressor. Outdoors in semi w/o a supressor you're better off with an AR.
My question is not whether a PD would allow an officer to use a particular round, just which weapon would be more effective.
The nice thing about the 300 Whisper is that you can fire subsonic rounds with a supressor, and still fire 125 grain supersonic rounds if necessary.
A subsonic .223 round would be worthless, while an AR firing supersonic rounds w/ a supressor would still be loud. The 300 Whisper seems to fill a gap between a SMG and an AR. BTW, both sub and supersonic 300 Whisper factory ammo is available on Midway.
Noticing the current trends it appears that the .223 is the end-all for tactical teams. MP-5s and UMPs have gone by the wayside, and the 6.5/6.8 are losing traction due to the ammo crisis and the Army's decision to stay with the 5.56.