I've gone from an Angel Tuned 156 2.4 JTD 10v to a 9-3 TTiD Aero with a Hirsch upgrade. On paper the difference is about +20bhp to the Saab, but the 2.4 should have a higher peak torque. In terms of how quick they feel, the 9-3 is consitently and undeniably rapid. The 156, when conditions were "right", did fly, but often it didn't feel like it was delivering all of it's 180bhp.
The TTiD just has a big fat wodge of torque from 1500rpm right up to 5000rpm, with no drop off in surge. This means it's in-gear pace is outstanding where I'd imagine* the v6 needs to be kept in the power band to deliver all of it's performance.
The 2.8T engines are very quick, later one's in the Turbo-X and Carlsson limited models are pushing out close to 280bhp with the turbochargers delivering serious low-mid range grunt.
*Never driven a 2.5 or 3.2 V6 or even been in one. So I can't compare apples with Apples here.
156 2.4 JTD 10v Veloce with Angel Tune (180bhp)