I got some clarification on the motivation behind forged components for the 3.8 vs 3.6 engines.

For the 3.6, we're obviously working on pushing the engine to extremes where we will need the strength of the forged rods and pistons.

For the boost/power levels we offer for the 3.8, we have found the stock pistons and rods to be sufficient. The main purpose of the 3.8 forged pistons is to offer a high quality replacement option for OEM pistons with rings that seal much better than stock. These pistons virtually eliminate oil burning issues that are not uncommon on the 3.8.

~Jeff