My girlfriend has a Volvo with a 2.5L 5 cyl (like in the Euro Focus ST only NA) It has a nice tone, but each cylinder still displaces 0.5L, so it isn't any deeper than a 2.0L, it just has more combustion events per revolution.
I like the sound of Nissan's old school (60's) s20. DOHC 2.0L straight six. It has 0.33L of displacement per cyl. It sounds like a little Indy car.
Same with the Carrera GT. I have seen a a few around here (3). They sound exactly like an Indy car. They have .57L per cyl with 10 cyl. @ redline (8400 rpm) it is pretty neat stuff.
I think a 2.0L 4cyl engine sounds nice, ours included. Put on the header, and stick on the Powered by Cosworth badge. I really don't think it will be loud enough to get you any tickets.
BTW
Top speed police interceptor Crown Vic= 129mph
Top speed of police radio (radio waves)= +/- 186 miles per second
Top speed of night stick= fast enough[chair]