You should study more from uncle Google bro...
M17xR4/R4 only support 1 GPU.

In stock performance 7970M and GTX 680M is almost same.

Performance per ringgit wise, 7970M is much more higher than GTX 680M.

Overclock wise, GTX 680M provide more room to overclock and become better than 7970M.

Heat wise, 7970M is generate more heat. But M17x's heatsink and fan is enough to supress 7970M temperature below 80C (If you use IC Diamond).

Maybe is not the best. But is the best that I used. Foreign sites discussion is about M17x R2 and R1. Usually is M17x R2.
Start from M17x R3, Alienware already abandoned xfire or sli support for M17x.

M17x R4 is all with triple heatpipe.

Only the new Alienware 17 come with 2 heatpipe (GTX 860M/GTX 770M) and triple heatpipe (GTX 780M/GTX 880M)...

Ya... this will increase the cost of upgrade.
Like if you want to upgrade GTX 770M/ 860M to 780M/880M, you will need to replace the heatsink as well if you found that 2 heatpipe can't handle the heat that produced from 780M/880M...

Is heatpipe la bro, not heat sink.
Heatpipe is the "pipe" on the heatsink.

Actually this all start from Alienware M18x R2.

Start from M18x R2, they provide 3 heatpipe for xtream edition CPU, but only 2 heatpipe for normal edition CPU.

As you know, M18x comes with dual graphics but they also provide single gpu configuration.

If you buy the single gpu configuration one, I have to say, very unluckly that there is no GPU heatsink will provide to you in second GPU slot.

If you want upgrade, you not just buy a new card, you need a new card, new headsink and new fan as well.

I did, but I am not applying white color.
My alienware is black, and I use back the black color coz I like black.. Hehe...

Reason that I apply the skin is because I know the soft touch surface going to peel off by time. The skin is just added protection.

How much you saw for that? May be I can get you a better price.

The seller in taobao that I used to deal with have tons of color and pattern
silver, black, blue, yellow, gold and many.

Mainly got 4 type of surface you can found which is the one I stated below
1) Solid color 亚光
2) Carbon fible
3) Metal 金属拉丝
4) Shinning matte 星光磨砂

It won't harm when decided to remove the skin off. It required some skill to apply the skin precisely.

The skin that I bought "C surface/palm rest surface" always cover the touch pad, but I didn't install it coz I don't like.

Haha... my laptop, phone, mouse, keyboard, car, watch all in black.

I send you PM tonight la. Hehe...

Very different, 1 mm difference in the front panel Alien head is very noticeable (Maybe I am too picky )

Test?
You can use a program called HWInfo to view or control your fan RPM

Bigger fan and better thermal compound. What else? Erm.. Better heat sink matetial.
Not much they can do actually. Unless using liquid cooling. Haha.

The starting price is cheaper than GTX 880M.
Actually already got people selling. But is MSI version. Not Dell.

GTX 980M Is below 3k.
GTX 970M is below 2k

GTX 970M perform better than GTX 780M and GTX 880M.

Maxwell (9xx) starting price is cheaper than Kepler (7xx, 8xx) cards.

I hope can bring some cheap GTX 780M and GTX 880M to sell here with lower price than my current selling price.

Hey Guys! Good news, I got one brand new unit of GTX 780M selling at RM 1399. 90 Days warranty. PM me if you interested.

Should be no problem. But can't expect too much if play in 1080p. 720p maybe

Which fan does not work? CPU or GPU? You can download a program called HWiNFO to manually spin your fan to see is it working.

When you diagnostic, the fan will spin right?
I believe the fan got feedback the pulse to motherboard when it spin and this is how and why the diagnostic says it is fine.

1st of all, you have to make sure the fan is really spin or not 1st. Second only think about "does it spin to full speed if CPU is too hot"

I see, you able to monitor the temperature right?
If your CPU is already in 80C and it still not at full speed. I suspect might due to the fan profile behaviour in bios.
You can try to take out the cmos battery and reset bios 1st.

If problem persist, update your bios. A little bit of risk to do that, but if you know exactly what you are doing, is completely no risk at all.

10 months, take it to warranty. if 3 time still got problem, directly email to Dell said you want to change a system. You told them you can't bare the lose that the laptop cost you every time it down. In fact, if you buy laptop from Dell website, they will replace you a new one if you complain. Provided they can't fix your problem.

Nvidia support optimus for this model. I think you using integrated graphics when play Dota instead of GTX 660M.

Right click->Run with graphics processor->High performance graphics processor

Or you can make Dota in always run with high performance graphics processor by adding it in to Nvidia control panel

Follow below link for more details

http://www.dell.com/support/article/us/en/19/SLN116149/en

Which model are you using? I can help you to find if you want.

Sounds like you always carry your AW18 around ya.