Well anything has got to be an improvement on todays current sheds. 
Converted Tranny's and Merc Sprinters around here. The embarrasment of seeing them 'rush' along on the moptorway at 70 mph with the 'blues' on, with everyone sailing past. 
So slow they could double up as hearses tbh, and have a ride in one and they may as well take you straight to the crem. 
What we need are BIG monster twin turbocharged and supercharged nitro powered V12 monsters with air suspension and 4wd capability. 
The Blues and Twos used on ambulances are intended to clear traffic out of their way ~ the vehicles and their occupants do not need speed for the sake of speed. They need safe and steady transport. Remember that those in the back are receiving treatment as they are being transported and frankly I would rather travel at 50mph whilst the paramedic is trying to ge a needle into a vein than travel at unsafe speeds risking God knows what en route.
If a patient needs the hospital that quickly then the air ambulance will get them there faster than any "BIG monster twin turbocharged and supercharged nitro powered V12 monsters with air suspension and 4wd capability"
Having been transported by ambulance whilst having a heart attack in the UK and in a similar condition through Paris in a French "ambulance" driven by a boy racer I know which I would prefer.
Incidently the Hampshire Fire Brigade staff that I know tend not to refer to "Blues and Twos" which many of them see as a brash Americanism. They refer to their sirens and lights as the "Excuse mees" because that is what they reckon they are saying
'Scuse me, 'scuse me, 'scuse me. And that is the point ~ they are asking you and other drivers to get out of the way. They are not trying to break a land speed record. ~ certainly not with several thousand litres of water in the back!