Considering this is going to be a business machine, I think we need to look at the priorities of this build before recommending hardware.
1) Reliability
2) Reliability
3) Fault Tolerance
4) Performance
5) Noise level
I understand that this poster is asking for quiet recommendations, but it is of the utmost importance that he or she uses the most rock-solid dependable hardware available to purchase. This machine will be
helping a business run and
putting food on someone's table.
I have a few suggestions that I would like to make based on my actual experiences with products.
1.) Like El Jefe said, a dual-core Opteron might be a good option if you're looking for the absolute best performance in the situations you describe. Considering you were planning on using a 4800+, take that money and spend it on an Opteron 265, 270, or 275. These run at 1.8, 2.0, and 2.2 GHz respectively and are based on the 90nm core technology for cool and efficient operation. Two of these would be nice, but this introduces the cost of yet another processor and server-grade peripherals. Please note that 2xx series Opterons can be used in a dual-CPU setup, so a future motherboard upgrade and additional CPU purchase can net you siginificant performance gains in the future when the price of the hardware comes down. The 1xx series dual core Opterons would be cheaper if they existed, but there are no plans to release them (soon), at least not as 940 parts.
2.) I recently put together a photo- and video-editing system using an Opteron 270 and
this motherboard. It is an extremely well-designed and well-built motherboard and is within the same price range of the A8N-SLI Premium. It uses the nVidia Pro 2200/2050 Chipset(s) with 8 SATA 3.0Gb ports, dual 16x PCIe graphics slots, and has been tested with the newest dual-core Opterons for stability and compatibility. The included chipset coolers are a touch loud but can be easily replaced with your choice of Zalman solutions. I would recommend the NB-47J with a quiet 40mm fan attached for maximum dependability.
3.) With an Opteron comes the requirement for registered RAM, which will be a little more expensive than standard DDR. I recommend ECC as well just to be sure that errors in your program output are kept to an absolute maximum of zero. Check
these out. They are not the fastest sticks of RAM on the market but they will be dependable in your intended system.
4.) The Samsung hard drives you picked out are fine. I have two of them in RAID 0 running in the computer I am typing to you on - no problems since day one, and they've been on almost constantly for the past 3 months. They're very quiet and for your purposes quite fast.
5.) If you do go with the Opteron, I suggest using the stock heatsink/fan until the warranty period is up for obvious reasons. I personally would not risk voiding the warranty on a $800+ CPU by using a non-certified heatsink. If the noise of that bothers you, replace the fan with something quieter. Believe it or not, the stock coolers for Opterons are very well-built. If you are intent on using a very quiet solution, go with something like the XP-90 w/Nexus 92mm fan, but PLEASE use something with a reasonable weight.
6.) The P150 will likely serve you well, but it is the only hardware I have mentioned that I have not as of yet used. I do, however, own a NeoHE 430 which is currently powering these very keystrokes. It is exceptionally quiet and has all the necessary connectors for your application.
7.) As for case fans, I would recommend the Yate Loon D12SL-12 orange fans run on a Sunbeam Rheobus controller. Nexus fans are too slow to provide significant air flow even at 12v; the D12s move 10cfm more at 12v and are still dead quiet at minimum input voltage. As an added plus, they are also cheaper. You can run them at 12v all the time through the power supply if you want to take the fan controller out of the equation to avoid possible fan/hardware malfunction due to improper controller settings or controller failure.
As for the suggestions made by others...
The ASRock Dual SATA2 mobo is nice, but has only one actual SATA2 port. That and there is no way I would ever ask someone to risk their business on a $70 motherboard.
Liquid cooling is great, but you NEED airflow through the case to cool the rest of the vital components (i.e. VRMs, nForce Pro/s, HDDs, GPU, etc). Like I said before, noise comes after reliability in a business system, so eliminating one or two near-silent fans by using liquid cooling isn't worth the hassle or extra money.
Quiet and reliable > silent and even
remotely possibly unstable.
No offense to anyone intended at all, just another POV. Some very knowledgeable people here for sure...
-DG-
but as eljefe said - a bios tweak is necessary if running 4 sticks.
The Ninja is definitely high on the list though. Might try moving the 120mm exhaust fan to the side of a Ninja to get both the CPU and the NB radiator.