"Then, why not install forged pistons instead of the stock pistons?
When I had massive oil consumption on my Viggen, this was attributed to blown pistons (this was not entirely right, but more later). As I had to spend quite some money, I investigated if forged pistons could be the way to go. A german tuner offered to install Wiseco custom forged pistons, but he told me that usually, 50.000 km on forged pistons would be a lot. It is not the piston that fails in this case, but the cylinder wall. This was backed up by a Wiseco rep I phoned: Forged pistons behave different from standard pistons concerning heat. If the car is still cold, piston tolerance is bigger. This will cause additional horizontal movement on the piston and therefore more wear on the engine. Not good for people using the car for a lot of short trips / city cruising.
Plus, if the piston is very hot, it can "mill out" the piston wall, which is softer than the piston material.
Generally speaking, one could probably say that the thermic balance of the engine is "disturbed" by using a forged piston, as the engine block was not designed to work with such a piston in mind.
The same was explained to me by Johann Heuschmid, former Saab factory tuner, and a Mahle Rep (Mahle is a South-German company which makes the stock pistons for the B235R).