I have a 1992 850GLT stock 20V 2,5 125kW version (european version as I live in Estonia). It does come more alive in 4000-5800 rpm range, but the difference isn't as great as on turbod cars. Most of the time just cruising around in 1500-2400 rpm range. At the moment looking for a 960 throttle plate ...

The 440 turbo can be made fast by using RichMod ECU. They are around in the Volvo 480 club europe. That raises the boost to 1 bar @ 3000rpm saving your cluch and gearbox. The result is around 175hp. I have a 480 turbo with that ECU and the car goes like a rocket.