I' m mulling over what release to settle on as well for 2003..........I just sold my Insatiable because I want to try some others like the " Insatiable 2" and Target 3 and Target 4 like you mentioned.
I like Carter releases, but I have shot the Tru-Ball Extreme and liked that as well.
I' m gonna have to line them up and keep trying until one stands out.

The main differences between the Carter releases you mentioned are the finger patterns..........like huntinhogs mentioned the Insatiable and Insatiable2 are for bigger hands, but they along with the Target 4 all have different finger patterns..........
The Target 4 is more of a straight handled " T" design like the Tru Ball extreme where the Insatiable has a much more " Swept back" finger pattern........the " Insatiable2" falls in the middle of the 2 being not quite as swept back as the original Insatiable but not as straight as the " Target4" . And like was mentioned the " Insatiable 2" also has an index finger hole rather than the open design of the others.

If you ask which is better on most forums.........Carter or Tru-ball you' ll probably get a 50-50 split. They are both good realeases you' ll just have to do what I' m gonna do and find which one fits you and your style the best.
Good luck