Comparison of two-weapon fighting feats

When a characters wields a second weapon in her off hand, she can get one extra attack per round with that weapon without any feat devotion in the characters level progression. She suffers a –6 penalty with her regular attack or attacks with the primary hand and a –10 penalty to attacks with the off hand when fighting this way.
Also, off-hand weapons only add half of the Strength modifier to damage roll; however, for Insightful Strike, the full Intelligence modifier applies to both weapons.
These penalties can be reduced in two ways:
*If the off-hand weapon is light, the penalties are reduced by 2 each.
*The Two-Weapon Fighting feat lessens the primary hand penalty by 2, and the off-hand penalty by 6.
*Improved Two-Weapon Fighting provides an additional attack with a -5 penalty AB, for a total of 2 off-hand attacks.
*Greater Two-Weapon Fighting provides an additional attack with a -10 penalty AB, for a total of 3 off-hand attacks.
*Perfect Two-Weapon Fighting provides the same progression for off-hand attacks as the character's primary hand attacks.
To sumarize, 
You do not need the basic two weapon fighting feats if your character has the Perfect Two-Weapon Fighting feat. However!,
You need the feat "two-weapon fighting" to reduce the -6 penalty to -2, even with Perfect Two-Weapon Fighting provided from the item.