Sorry OP, wasn't aware you couldn't get the Brera in 1750 form -- they exist in Australia but are rare.
There is no 5K rev limit on the 1750. The beauty of this engine is that with the low down torque you can drive it like a diesel (though it will NOT return diesel-like fuel consumption if you do); but if you choose to rev it out you can without the power falling away. Otherwise there would be no point to the 1750 over the diesel.
Not only does it thump out a V6-like 236lb ft of torque at just 2000rpm, but the power peak doesn’t just come and go. Instead, it holds its torque peak for an eternity before the power takes over at 4750, then remain in charge all the way to 5500rpm.
: Alfa Romeo 159 1750 TBi Review | Autocar
Agree entirely with Malheus about second gear. Like a Moto Guzzi that's where the torque kicks in. TBi will happily take off in second too.
Regarding weight -- even if the engines weigh the same and I doubt they do, the chassis was lightened in the 1750 era:
Alfa loses weight for Geneva | Autocar
The ride is streets ahead of other 159s I’ve experienced, and the new engine helps here too, as it has been designed to be as light as possible – this 1750 TBi unit weighs 110kg less than the V6 and over 140kg less than the popular 2.4 JTDm diesel. With the mass over the front wheels reduced and better damping, this car doesn’t suffer from the terminal understeer found in other 159 incarnations.
Ride height? Well, Ti-spec cars are lower anyway including the JTS-powered ones. They can be a pain to navigate over some gutters, just like any other lowered car. Trade off is of course lower COG and better handling.
I think the 2.2 JTS is a perfect candidate for an Autodelta supercharger if that's cost effective; i.e.: you'd need a low cost car and an awareness that the supercharger might cost same as the car.
I can tell you there is no way I would switch from a TBi back to a JTS, and haven't encountered anyone who has. Can't recall any forum correspondents switching from a TBi to a V6 either, even though you'd make money on the swap. And yet to meet the Alfa specialist mechanic who thinks the JTS is a better engine (we had a 939-series tech day last week in Melbourne).
Re noise, the TBi sounds like a hairdryer if revved at idle. Under load it's simple -- push throttle open and appropriate exhaust noise will occur. So no joy poodlefaking in the high street but rewards the aural senses when being driven in a spirited fashion. I am coming out of warranty soon so the option of an aftermarket exhaust will open up as well.