Nope, you can't do that, you can't put 6pin connector in 8pin hole. You should have gotten 2 of 6+2 pin converters in box with that GPU, so all you need is to slide off two pins of one converter. I don't remember whether they should be on the right or left side, but if you name side which goes into GPU "the bottom" you need to push those pins upwards to slide them off.
Edit: scratch that, I just remembered that vapor x has two 8 pin connectors, forget what it says just connect those two 8 pin connectors to your GPU.
My power supply supports 30 amps on the 12v rail so am I good to have 2x 4-pin to 8-pins going to the gpu? And can I run the 4-pin molex to 8-pin on the same wire from the psu which has two molex sticking out?