Can't believe this thread is so empty. Seems like this is all very important (and organized) information.

Btw Chittagong, we're these measured with the X51 standing upright, or lying flat?

Yeah I know, and it doesn't even take that much work to measure, just getting Open Hardware Monitor and playing a game... Especially the CPU idle temp is interesting to me. Hopefully people will post theirs.

Mine was measured lying flat. If I recall right, it's a marginally cooler position, although the difference wasn't huge.

I have the same CPU temps as you on my X51 .. vertical orientaion.

CPU Idle Max: 60 C

BF3 Max (high): 73 C

@Chittagong

I also have installed the same card (HD 7850) and have almost identical temps as you've displayed (idle and in stress) using Open Hardware Monitor.  The Temperature#1 reading is also the same as you've shown and idle's right around 66c.

OK, My turn.

Specs:

• CPU - i7-2600
• GPU - Sapphire HD 7850 OC (920/1250)

Notes:

• Horizontal/lying down position.
• Inverted case fan mod.
• Stock heatsinks/fans.

-------------------------------

Temps (Max)

Idle:

• CPU - 54c
• GPU - 49c

Gaming/load (Crysis @ Very high settings - 2 hours):

• CPU - 67c
• GPU - 76c

Burn-in test (Prime95 + Furmark - 15min):

• CPU - 84c
• GPU - 92c

-------------------------------

In theory, my 7850 should run cooler than Chittagong's 7870. But as you can see, every x51 setup is unique. Haha.
But's the good news is, my 7850 runs relatively cool (< 80c)  during load gameplay, which I am satisfied with.

Next time I will try to change up some fans/heatsinks here and there to see if I can somehow improve my temp scores.

Just installed the Zalman CNPS8900 Extreme (Arctic Silver 5 thermal compound):
http://www.frostytech.com/articleview.cfm?articleID=2657 

From what I know, I am the first to do this mod.

Here are my updated results/temps: 

Specs:

• CPU - i7-2600
• GPU - Sapphire HD 7850 OC (920/1250)

Notes:

• Horizontal/lying down position.
• Inverted case fan mod.
• Zalman CNPS8900 Extreme heatsink (Arctic Silver 5 thermal compound).

-------------------------------

Temps (Max [Difference from stock heat sink])

Idle:

• CPU - 53c [-1c]
• GPU - 47c [-2c]

Gaming/load (Crysis @ Very high settings - 1 hour):

• CPU - 64c [-3c]
• GPU - 70c [-6c]

Burn-in test (Prime95 + Furmark - 15min):

• CPU - 81c [-3c]
• GPU - 93c [+1c]

-------------------------------

Conclusion:
This isn't the number #1 low-profile heat sink on FrostyTech for nothing. I was initially anxious about the heatsink not fitting in, but it actually fits perfectly. The distance from the heat sink to the case and the RAM is less than a half a cm away. The only "mod" I needed to do to fit the heat sink in was move one of the cables out of the way.

Here are some pics of the Zalman in my X51:
https://docs.google.com/open?id=0B98pN46IT15vMmxFRlUtZ0syVHM

As you can see from the results, the the idle temps are cooler at idle. Gaming temps are also noticeably lower. And I would personally say it's slightly quieter than the stock fan as well.

If you have the extra cash and want to upgrade/mod your X51, I highly recommend this the Zalman CNPS8900 Extreme. Please note that there is also a CNPS8900 Quiet for those who want an even quieter fan. I'm not sure how well that handles the heat, but at least now we know it will fit.

eBay (cheapest option):
http://www.ebay.com/itm/Zalman-CNPS8900-EXTREME-CPU-Cooler-110mm-Fan-Slim-Low-Profile-4Pin-Blue-LED-/330693860114?pt=US_CPU_Fans_Heatsinks&hash=item4cfee3db12#ht_5768wt_881

Amazon:
http://www.amazon.com/Zalman-CNPS8900-EXTREME-Cooler-Profile/dp/B0077POH4Q/ref=sr_1_2?ie=UTF8&qid=1337392188&sr=8-2

Newegg:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835118127 

Hello,

here are my temps for my Alienware X51 with the GTX 555 OEM and I5 Model:

Idle:

◦CPU - 59c [+1c] (after 3 h Desktop)

◦GPU - 49c [+8c] (only Windows8, i think its the new Hardware accelr., on Windows 7 +2C)

Gaming/load (Guild Wars 2 @ Ultra settings - 1 hour):

◦CPU - 67c [+2c]

◦GPU - 78c [+1c]

Burn-in test (Prime95 + Furmark - 15min):

◦CPU - 79c [-1c]

◦GPU - 81c [-1c]

Hey guys, I created a Wikia page, as this information would be great to have in that page or at least have a link pointing to this forum. Please let me know what you think about it!:

alienware-x51.wikia.com/.../Alienware_x51_Wiki

Hi Van1ty - did you need to do any soldering or just simply open and change fan to zalman?

This is my temperature with Prime95 for 10 minutes.