Hellu is Blue Lady :3
I have repasted my G750JX multiple times, around 4 times over the past two years I've owned it. I live in Australia, so it gets very hot here, so apart of my conditioning routine to keep my lappy in tip top shape as if it's brand new is repasting every so often during the summer time.
Your lappy has around 38 chips roughly that must be in contact with the heat sinks inside, 37 of them being the GPU itself.. while the CPU of course is one chip alone, the die. ;d
It is quite the advanced task, my first time doing it took me 4-5 hours to complete, as the stock thermal paste really is a b!tch to get off of the PCB of the GPU. It's very thick, and very gummy.
Anyhow, if you're going to replace your GPU paste, you'll want something like K3-Pro, the thick thermal cement-like stuff, and a paste of your choice for the dies themselves.
What you saw when you disassembled the unit was the stock thermal err.. mess.. as I'd like to call it, basically it's just a thick gum that goes over the sink in a big strip then slops over the chips. It's a contact none the less.
Using Arctic Silver 5 on the chips and so on MAY BE a bad idea, I believe the metalic components in the arctic silver can induce capacity and possibly short out something on the board, however the chances are quite minute, though it is still a chance, correct? ;d
Another thing to worry about is, Arctic Silver may not be as THICK.. or 'viscous' as the official term is, so it may run or grow thin and break contact from the chips to the heatsink.
If this happens though, don't worry too much!! It won't get on your board. Most people forget that the heatsink (once assembled again) is UP SIDE DOWN inside of the laptop. So, nothing's going to smear over the board if it does happen to go runny.
Anyhow, I am sure AS5 is thicker than the carbon pastes I use, I used MX-4 for my dies and K3 Pro Gummy for my chips.
P.S. Don't worry if your chips get to 80*C under load, it's not nice, but it's fine to function under those temperatures for a limited time.. try to stay under an hour. If you reach 85*C that's bad.. too much.. the solder that bridges the GPU's die to the board may start to warp.
The manufacturer says the chips can withstand up to 100*C but 80*C is where you don't want to cross. I usually monitor my temps and stay below 75*C when I can.
In the end, as far as I'm aware, the sink is perfectly level with the chips on the GPU, make sure there's not a chip left pasteless. :3
❤