The downside is a reduced rod ratio, reduction in amout of revs engine can make safely etc.

The upside might be more BHP and torque but with spikey torque it just breaks gearboxes and looses traction etc

It will also move the power band further down the rev range and make the turbo spool up quicker

From a personal point of view I have chosen to de-stroke my engine from a 2.1 to a 1.8 as I'd rather have the power band further up the rev range and less torque to make the car more drivable

You cant beat cc's for power though

IMHO