The 1750 is already turbo charged so how much more you going to squeeze reliably.
The 2.4 you can take from 210 to 260/ 70 with a dpf removal and remap
The 1.9 diesel can go from 150 to 205
Petrols such as the 2.2 only get a 10bhp increase from remap.
Of course intake and exhausts etc will improve it a bit.
Ifnyou want to spend bigger money superchargers are available for the petrols and I am sure you can turbo one of them.
I'd love to put a rotary engine into one - imagine 250 - 300 bhp in a 159 with a light engine
. Would help the handling also and 8000 rpm also good
Mind you a v6 sound would be nice