18* is good. I have heard/seen most guys say ideal for power to be at 21*, that is running at the top end and knowing everything about the engine and how it'* running.
I set my motor up on a 2.9" pulley, planned a 2.8" for daily driving once it was tuned and ready for it. In the box I have 2.5", 2.6", 2.7", 2.8" and a couple others. A friend gave me the 2.6" and 2.5", doubted I'd ever run them. On the Gen V a 3.4" is roughly equivalent to a 3.2" on a Gen 3, airwise. Since both chargers push the same amount of air, that'* the cooler efficiency gain. I can't quite imagine the 2.5" on a Gen V.
00 Regal GS: All kinds of cool stuff.