No offence to you mate but that is utter bullshit showing he doesn't know what he's talking about.
1) My motherboard at the moment is an 'ASRock 990FX Extreme3' with 3 x PCI-E 2 slots.
It supports 3 way SLI/Crossfire with the full x16 bandwidth each, motherboards haven't been made like he explains with the top slot having x16 bandwidth and the bottom slot only having x8 for over 8 years since before the 'ATI 580X' chipset (released in 2006, more than 5 generations ago), which was the first chipset that allowed x16 + x16 on both lanes meaning full power Crossfire (ATI dual card) systems were now possible.
This meant that the days of Master and Slave graphics cards were over, the first graphics card that supported this technology was the ATI HD3870, I know this for a fact because this PC was originally built around that platform, I was one of the first if not THE first person in the country to own a fully working x16 - x16 Crossfire system because I spent around £600 pre-ordering the ATI cards and motherboard from Hong Kong before the new technology was even out on the market (by at least 2 weeks in Europe).
2) Software at the driver level overclocks a graphics card, this doesn't come into play until the PC boots up to a Windows desktop then the graphics card driver software kicks in shortly after with the 'Startup' programs allowing you to do this.
You can't boot up into windows and overclock the card with software if the card is dead in the slot preventing this.
3) There's not a single or dual graphics card setup invented yet that is bottle necked by the PCI-E 2 x16 specification, not even dual Nvidia 'Titans'.
His analogy is laughable.
4) Every single graphics card manufacturer ever has used cheap crappy thermal paste on every graphics card ever sold, just like every console ever made and every PC processor/heat sink ever made, because they're mass produced units.
I personally use professional thermal compounds like 'Arctic Silver 5' that is made from 99.9% silver costing around £10 for a 3.5g tube.
Every time I buy a new processor or graphics card first thing is it gets stripped with a professional solvent cleaner and Arctic Silver applied before it goes near the machine.
I never have and never will run or install components with standard shitty thermal paste, even my Nintendo Wii has silver paste applied!
I don't know what your mate does man but he obviously doesn't know his way round a modern professional rig.
You can tell him I said that too.