Unfortunately that's a common misconception.
Modern cars use the full capabilities of the turbo that they're supplied with - the turbo is properly matched to the application and power level for which it's specified. If the engine is designed to make 120bhp, for example, the turbo will be specified to provide enough air flow for 120bhp + a small margin for part to part variation + some margin for altitude (but this varies from manufacturer to manufacturer). Manufacturers won't pay for a larger turbo than is necessary, and favour smaller turbos for less inertia and better response.
Asking too much more of the turbo could cause it to overspeed, that is run faster than the specified limits. If Alfa had wanted the engine to make 40bhp and 60Nm more they'd have made it do it, and spent 3 years running durability tests, etc to make sure it would be reliable at that power output.
Be careful is all I'd say - you don't get anything for free.