Billyray, just a few notes first of all regarding the PLX chip in your Maximus V Extreme. Your motherboard is a 1155 platform with a Z77 chipset. Amongst other things, this means that the CPU/Z77 can talk to 16 lanes through to the PCIe type device. As Asus wished to offer more lanes to allow for 4 way SLI, they included what we call a PLX chip on the motherboard. The actual PLX chip used is a PLX PEX 8747.
This allows the MVE to run 32 lanes (at PCIe 3.0)

However, it was up to Asus to design how they were going to do this, and if we read the manual carefully, we can see that the lanes that use the Z77 only (termed native) are the Red slot 1 (named PCIe 3.0/2.0_x16/x8_1 in your manual), and the Black slot 2b (named PCIe 3.0/2.0_x8_2B in your manual).

The way they have designed this area means that if you only use the slots that use the 16 native lanes (the ones going directly to the Z77), the PLX is not needed, and in fact will not "turn on". If you happen to use another slot with a single (even if it's a dual on a single), apart from the two above, you will turn on the PLX Intergrated Circuit. When the PLX chip is running, it consumes about 8 watts of power typically. Not much, sure, but the heat generated in a small 27mm x 27mm chip could see it rise to 50C.

Given your choice of Video card, you can now see the reason why you would be well advised to use one of the two slots mentioned above, so that you run "native" lanes, rather than turn the PLX on. I would recommend Red slot one, because, as you can see on page 1-26 of your manual, the first red slot will give you x16 3.0 PCIe, while 2B will give you x8 3.0 PCIe. I would only use 2B if there is a fitting problem...praps interference with other hardware.

Two other matters you mention. The first is the positioning of the PLX.......it's not under anything, but is positioned between the 3rd and 4th red PCIe slots, just above the small black PCIe x4 slot. The second concerns the "cutoff" temperature of 105 degrees. This is associated with the PLX, but is also the temperature, that if the CPU gets to, it will shut down.

Hope this assists.

what if im running my ati 7870 in 1a and 2a crossfired ? why is my plx temp go to 50c or above when im gaming? right now on idle it says 47c. why is that can I make it run cooler ? Ive ordered a water cooler block for my board that asus recomends instead of the pipe cooling thats installed will that help? Im koolance water cooled with resevoir rp-452x2 and dual 450 s pumps and 1/2 id 3/4 od hose and 2 radiators far as cpu. also have a 1k mushkin joule split rail power supply . ,y mobo dont go aboove 33c and cpu dont get aboive 45c at idle 33c