oh yeah that's right, 19. I only remembered it was less than 20.
I never drive a regular Smart before, so I cannot really compare performances like you do, but like you said, the car is quick. I once loaded the car (removing subwoofer of course) with a 28 inches suite case and a small carry-on bag and one 230lbs adult, and I am 190lbs, the car is working without a sweat. Sometimes when I downshift hard, I can even hear a small crack noise from my Brabus exhaust. I still feel bad that we don't get Brabus tuned in US.
You would probably never describe the smart 451 as "quick." And in my opinion, that's okay. Understanding the smart 451 was difficult for many American drivers because they never experienced owning a 1.0L 3-cylinder car before. If they did, the smart 451 is a sports car version of that engine class. The single-clutch manual was difficult for many, but in my opinion, those folks lacked the skill to control the transmission. So they blamed it. Single-clutch manuals have been used on some older high end sports cars, some commercial trucks, and other vehicles.
They were often the source of complaints on those vehicles as well, the only difference is the high end sports cars will always get a criticism pass due to exotic appeal, and the commercial big-rigs will always get a pass because they are just big rigs afterall. But those transmissions were used for engineering / performance benefits relative to the design of the vehicle. It just took drivers willing to understand and agree with it, then once they agree they can learn how to coordinate their foot pedal position to control the transmission's shift behavior.
If they master that, then the smart 451 will either downshift, upshift, or stay in gear however the driver intends for it to. And then suddenly the brilliance of the smart 451 is obvious. Throw in some bobbing and weaving handling and you'll notice how responsive the smart's 451 chassis is, and it becomes a fun errand running car with kart-like responsiveness. That's awesome in tight traffic, and gets away with maneuvers no other vehicles can get away with. Powerful cars out accelerate you, well designed cars can out maneuver you. The smart out maneuvers. That's the idea.
In regards of MPG, I am averaging around 42ish on my daily home to work commutes, mixed of highway and local and I am averaging 36.8 on my total 5,000 miles per trip computer. I hit 99MPH multiple times, it is very interesting that my cluster shows a top speed of 130MPH, but when I hit 99MPH, it only goes 2/3 of the numbers. This car is my first micro/small/economy car, I am really happy with its current MPG, because all of my other cars are around 20 to 25 to the best.
I don't think I would ever want to hit those speeds in such a short wheelbase car. 96 is more than enough IMO. You can easily get tickets going 80, and the smart 453 is easily powerful enough to live at 85 mph's. It'll climb hills at those speeds if you want it to. It's nice that you can go so fast, but please be careful. This car is powerful enough to get itself into trouble, unlike the smart 451.
The smart 453 shows signs of overpowering its chassis with engine power. It can get you into trouble the chassis won't get you out of. It's why the ESP on it is so aggressive. Gotta protect the driver from him/herself. The chassis of the 451 gave the driver confidence to toss it around at any speed it was capable of achieving.
However, the 453 has reached the next-level. The engine and transmission is high-tech, just limited in displacement at .89L. It's the only "weakness" relative to bigger vehicles on the road. The other vehicles on the road can only rely on larger engine size and the horsepower/torque figures they put out, to beat a smart. Same went for the 451, however the engine was naturally aspirated in those so even some larger cars could claim a turbo and dual-clutch as an advantage. Not anymore. smart's 453 has it too.
And that little body is so light, it doesn't need to develop as much power as larger vehicles anyway. It's easily more maneuverable and capable of thoroughly embarrassing large muscle cars if racing through traffic (don't do it, not recommended).