6+2 Video Extension Cable...

I'm looking to get some of NZXT's premium cables and I want to be sure I'm getting the right cables for my GPU. I have GTX 680, which requires 6 and 8 pin. I have a straight 6 pin and 6+2 pin connected from my psu. Now, NZXT offers a straight 6 pin to 6 pin video extension, which I believe is fine for the 6 pin, but I've heard their 8 pin to 8 pin video extension doesn't have the right headers. (I saw one review say the headers are for a mobo.) They also have a 6 pin to 6+2 pin and I was wondering if it would be safe to plug just the 6 pin of the 6+2 from my psu and then plug the 6+2 on the NZXT extension into the 8 pin on the GPU.