Well, being a COP, I can tell you a few things.
Turbo applications don't work for police. We were given a Turbo Volvo for a while and it didn't work. Too much LAG and we don't maintain vehicles enough let alone with Turbo. Get if fixed, get it fast and get it cheap. With all that stop, go and hard driving, we'll burn those turbo's in no time.
Even though the 4.6 was underpowered for the current Vic, it is bulletproof. Reliable and tough, needed about 60 more horse's to do the trick, but those cars start all the time and you can absolutely pound the [censored] out of them. And they will run on anything. Cheap oil and cheap gas, not premium fuel for turbo's and synthetic.
As per synthetic oil in our cruisers, good luck. Your lucky if we change the cheap bulk in them every 10,000 Km's. I think that you will see a lot of agencies going with the rear wheel drive Caprice. Normally aspirated is better suited for police/taxi applications.
And cabbies, who buy the most our our used cars anyway wont touch a used and abused turbo. But they will buy an abused V-8.