To be fair its the Ultra long gearbox that lets them down. But saying that even with the extra weight and long box they are still faster than a EM1 Coupe. Probably on par with a B16 hatch but off course not handle as well with the extra weight. They do have a good bit wider track than an EK4 so guess that will help.
End of the day you can make a car as fast as you like. For what you pay for a half decent MB6 you will have plenty of cash to upgrade, in comparison to buying the likes of a half decent EK4 or B16/18 swapped hatch for much more money.
Out of the box I would class it between a UK EK4 and EM1 Vti for pace wise. But far more practical than either, more potential having a B18 already and already equiped with bigger 282/260 brakes.