Dude, I'm telling you that the vBIOS will need to be modified in order to make this work. The wattage needed to push the 670MX is lower than the 780, by a lot. You'll undervolt the board if you don't look at changing the power throughput. My G75 is through Xotic too, and I got lots of bells and whistles with it but trust me when I tell you this; upgrading the video card in this laptop isn't worth the trouble. You'll need to modify the chassis, you'll spend nearly $1000 on the MXM card alone, your cooling won't be up to par, you'll need a custom vBIOS for certain (75w vs. 100w), you might even need a special PSU (like 200w or higher) and in the end, if it works, you'll have at best something with questionable reliability and stability issues.
It's your time and money but you are going down a road others have tried and I have not seen one that came back with a working laptop. For the same money you can set up a dual mSATA raid 0 in a single HDD caddy or something else that will give you plenty of performance without the headache of hexadecimal editors and nvflash.
You said that when you overclocked your card it crashed (it's not the drivers, BTW). That's likely due to the card undervolting because the increased clock increased the power demand. The 180w PSU that comes with our laptops is right up against the minimum needed to run everything when it under full load. You're hitting a power bottleneck when you overclock past a certain point, a custom vBIOS is the only way around that. Not BIOS, vBIOS. It's the firmware on the video card itself that you'll need to change, not the motherboard BIOS. Another thing is that the Intel HD graphics is disabled on the G75. That's why we don't have Optimus. The GTX 660, 670, and 670MX for our laptops don't have the pass through for the processor to work as a GPU. It's physically impossible for your processor to work as a video card with these laptops. What you're seeing is your card getting unstable under heavy overclock, crashing and then recovering (because its built to do that).
Another note is that swapping in a new wireless network card, that works perfectly fine with these laptops (I don't have an Atheros either, I went with an Intel card too) is nothing compared to this kind of undertaking.
I can't stress this enough - don't do it bro!
