I've modified a lot of ROG Notebooks over the years and I understand the frustration and experiences here so I'll shed some light on this for everyone.
Every model has it's own quirks, and with that one critical piece is the root of the commoner - temperatures. This ALWAYS stood out the most to me in every ROG notebook disassembly I've done, and that's the heatsink assembly is always resting cockeyed! Due to the design (if 3DVC model) and overall dimensions ASUS use for their G751 and G752 heatsink assemblies (which have the most problems with temperatures). There is so much room for error in handling and assembling these notebooks because of their massive one-construction-design heatsink assemblies.
Are CPU/GPU temps high? Hovering near throttling limits of 95°C at stock clocks even? (100°C if temp activation offset in BIOS set to 0). Performance not as advertised? Feel like your money went to waste with your ROG purchase? Absolutely understand the experience! The problem is that ASUS doesn't train technicians to "troubleshoot" these RMA requests about your notebook problems at their service centers. In fact they just replace your recently purchased "new" parts with refurbished ones so the turn around time is more desirable to you (very rarely are new parts used as replacement in this process).
Does the heatsink assembly make proper contact? It requires a disassembly and a checklist to complete - order of process - easiest and cheapest options first.
I've had to bend so many heatsink assemblies at their heatpipes ever so gently so that they rest as flat as possible on the components below in almost every ROG Notebook I've purchased. I've gone even to the point of using a dremel tool to reduce the mounting points (before affecting threads) of the bottom bracket to lower the heatsink assembly that much further downward. To go as far as even removing the brass plated prong springs around the VRM area of a GPU in the newer G752 models and visually noticing the heatsink assembly making better contact. Sometimes it's not just a repaste but further intervention!
Is there ever a problem with just the heatsink assembly? Not usually, in fact I was recently helping a fellow ROG member out who had temperature issues. Having gone down this road before and through the extensive list I've made in the past like checking fans (ramping speed up with EC registers), repasting with better TIM, doing an intake mod, even dremel tool mounting points, readjusting heatsink assembly - rinsed and repeated - to addressing the higher temps it did, but the gains of the lowered numbers weren't as beneficial as other attempts. Why is that you might ask? As my last suspicion, it was dud heatpipes in the heatsink assembly. So another one had to be purchased and that solved everything! Things like this can be overlooked by ASUS employees who work on these ROG Notebooks because it's time based! I've mentioned it before and I'll mention it again, they need to further educate their division and teams who handle their ROG Notebook lineup, so that down the chain, these problems can be easily addressed!
Take a look at the newer G701VI model, the entire bottom part of the chassis can now be removed exposing the entire heatsink assembly, instead of an entire notebook disassembly to get there. This makes for easier upgrading and maintenance now... hopefully they stick with this kind of design in their future ROG Notebook models.
Typically, temperature related issues are almost ALWAYS tied with whoever assembled your notebook. Sure you might get horribly binned CPUs and GPUs that have higher ASIC voltage, but improper care with handling and mounting of the heatsink assembly, to the amount of thermal compound used throughout the notebook assembly, is the cause of it. In fact, why ASUS doesn't even properly test each unit with an ACTUAL stress test to stamp it with a seal of approval based on the report BEFORE allowing into the distribution channel is beyond me.
Most people don't have the necessary tools, skills or even time to take on doing these kind of modifications to avoid going through RMAs even (and they shouldn't have to as a customer), as RMAs too present a problem if the ASUS service technicians aren't actually addressing the same hardware if they are simply replacing it with another working one - refurbished - which may have it's own problems and so the cycle continues through further RMAs. It goes deep and because ASUS is such a big company who sells in volume (cookie cutter), despite each person and their experiences, whether negative or positive, doesn't mean their notebooks are terrible just because of what is posted on the forums. A lot of people who've had positive experiences aren't likely to register here to post how well their systems are running, but some do.
The point of all of this was, there are ways to combat these issues should you be the DIY type, or if RMA is an only option for you, to understand the leniency you must have in the return of your new to
product. By going with another brand of notebook, you take on the problems inherited with it. Some people just get better assembled notebooks than others do. Surely do extensive testing after purchasing and depending on the store or online vendor, if it's not performing as advertised in stock configuration, return it or exchange it for another one. Not much else can be done about it.
EDIT: After all my G752VS cooling mods and heatsink assembly adjustments, just to reference for anyone else curious about potential performance, running FIRE STRIKE at "STOCK" configuration (and a few open applications). This is the result for CPU and GPU temps:
http://www.3dmark.com/fs/11059699
No, the notebook was not cooled by an AC unit or placed in a freezer; The G752VS overclocked FIRE STRIKE results are in my signature.