It "gives" you innate 5 HCI, stacks with items. Also gives you a 50 HCI cap.
Means if you are naked your garg has 5 Hci, if you have 45hci on your suit, you now have 50hci and if you put more than 45hci on your suit you will still be at 50hci no matter what.
In short
Gargoyle has...
5% bonus hci AND 50% hci cap.
However I have to say this, if you think that 5hci will make up for the ****tiness of throwing, then you are terribly wrong.