you can make 250 n/a on a 6er, it just takes a bit of money and know how. Ive seen a few on here back in the days it was mainly a V6 site with 230/240hp still a 3.8L.
id go with a 4.2L and a really nice top end combo from any of the above mentioned vendors, it will be a very nice naturally aspirated combo, and later on if you decide to go forced induced, it will be that much better, though you will have to decide now on if you want naturally aspirated, nitrous
, or blower grinds on your cams.
simply adding a SC or TC will not adversely affect the livespan of the motor unless you forget to change oil. Trying to run ungodly amounts of boost and/or not tuning the setup by a reputable tuner will. DarkShadow is running i believe 11psi ish on a turbo setup on his 3.8l with a stock motor/heads.