100+ in a Crown Vic? No way... sloppy feel of the steering in one of those babies... unless they've improved that greatly... Just way too easy to oversteer in one of those base fresh off the assembly line. Maybe if it has a sports package that inproved road feedback and feel....
I can and have done well over 100mph, but on a public road in traffic, 80ish is tops for me... of course if I lived out west where the Highways are all flat and straight and drone on forever I might be more comfy at higher speeds... here, where you are going around, over or through a mountain to get anywhere, 80's is fine.
For '03, they finally upgraded to a rack-and-pinion setup. It's WAY better than my '97.
Mine's a '95 with 300,000 on it. No slop in the steering, highway ride is excellent - and I grew up driving "fine European Import" type cars as well as competition equipment.
If you want to go 100+ in a Crown Vic, it is easily done:
Crank "caster" up from 5.5 to 7.5
Install Bilstein HD shocks and (preferably) cop springs
Use speed-rated tires (W or Z) with 40-43 lbs pressure
Be certain ball joints are healthy (and if need be, install Moog)
After that, piece of cake. Of course, the civilian version will cut out at 107, but you can buy a salvage cop computer and increase that to 129 (or slip your Ford guy a 20 and he'll set you up).
OTOH, I don't see a need to go that fast. Still...