Okay, let me first preface by saying: I've read tons of guides (on this site, and elsewhere in internet-land), I've crunched numbers at the various power supply calculators, I've debated til kingdom come already in my own head... But now, I'd like to turn to the community for suggestions.
Here is my current system:
CPU - AMD Phenom II x4 960T "Zosma" (I haven't attempted unlocking the extra cores yet, and haven't overclocked anything either)
Mobo - ASUS M5A97 AM3+ 970 chipset
RAM - 2x4GB G.skill DDR3-1600
Optical - ASUS DVD±RW (SATA)
Sound - on-board, TBD if I'm going to invest in a standalone card
Video -- to be upgraded as soon as my IRS refund gets deposited (hopefully later this week)
PSU -- a Thermaltake non-modular 600W model, also to be upgraded with my IRS refund
Now, I'm all but set on the XFX Double D HD-687A-ZDFC... And I know what technical specs I want in a new PSU: modular, 80+ certified (bronze or higher), multi-GPU capable (has to have at least 4x PCI-e power connectors), and Active PFC. Unless someone can suggest a better sub-$175 card that will fit into my Antec 300 Illusion case, I'm going to buy the above-noted XFX Radeon 6870 card soon with plans to expand to Crossfire in... the future (a month, or three). And yes, I'm open to suggestions.
But I'm really looking for input on picking a power supply. It needs to be powerful enough to run a crossfire setup and leave a little wiggle room to make me comfortable. By my calculations ~750W of 12V power should cover that nicely. I've read certain items that make me want to steer away from a single-rail @ 70amp type of model, and other certain items that make me want to steer away from a multiple-rail type of model which each real and/or virtual rail having ~30amps.
The Raidmax RX-850AE caught my eye as meeting all those technical desires and power needs I believe I will have, but after input overload I'm looking for confirmation or a suggestion of a better route to take.
For a system using two Radeon HD 6870 graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 43 Amps or greater and have at least four 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.
I would suggest adding at least another 5 Amps to the combined +12 Volt continuous current rating to handle unlocking and overclocking of the CPU.
Avoid Raidmax. There's a reason why they have a shorter than industry standard warranty.
Antec, Corsair, Enermax, Seasonic, XFX are the top tier brands but you need to do your research on the specific model(s) that you are considering.
@Silvune - My general personal mantra is "best bang for the buck." Though, if I were to set a dollar limit it would be >$150 if possible.
@ko888 - good suggestion and advice.
As to that 850W Corsair suggestion, I absolutely appreciate the suggestion of going Corsair, but after checking the specs... I don't prefer a power supply that's only semi-modular. I don't really want that vomitous, Cthulu-looking mess of permanently connected cables cluttering up the inside of my case (that's the entire reason why I'm upgrading the Thermaltake).
I don't need 2 floppy power connectors. I don't want 8 SATA power connectors (presently, I need only 4). I don't want 6 molex / "peripheral" power connectors. (I do have two case fans which use them, but I'd much rather replace those fans entirely to do away with that dinosaur of a connector.)
Sorry, I know that comes off harsh. I don't mean it to sound like an attack. I just absolutely know what I want to have if it exists.
Same video card as I'm wanting, plus higher amps on the 12V rail...
Pros / Cons to either the OCZ or the Corsair HX750? I love and appreciate all input the community will give -- I'd rather be picky now than end up choosing a power supply that'll bite me in the rear when all is said and done.
Some have complained that the OCZ ZX Series 850W's (20+4)-pin ATX main power connector cable and the Dual (4+4)-pin CPU power connector cable are too short when used in computer cases where the power supply is bottom mounted like your Antec 300 Illusion.
You may have to resort to using extension cables depending on how neat you want your cable management to be.
All members of the OCZ ZX series perform quite well.
However cable lengths on the main connectors are 55cm, whereas on the Corsair they are 60cm (Corsair claim they are 65cm, but when review sites have actually measured them they all consistently say 60cm).
The Corsair HX 750, both as a unit and the OEM (CWT) have built a reputation in terms of build quality, but I don't think the ZX series (OEM - Great Wall) have done the same thing (yet).
The Corsair HX 750 and the OCZ ZX series have the same fan: Yate Loon D14BH-12. Which has a maximum fan speed of 2800RPM.
The HX 850W version had it's fan on full load measured spinning at ~1300RPM. Idle has been measured at ~900/1000RPM tho.
The OCZ ZX 1250W, is the only member of the ZX series, AFAIK that has had it's fan speed/curve measured (by a site I don't know that well: hardware-academy.org). It measured 600RPM at minimum and 1500RPM at maximum load.
Out of the two I would choose the HX 750 because of the longer cables, it potentially being quieter and a better reputation. But that is before I consider the price, as at $120 (effectively) that makes the OCZ ZX very competitive.
However as I'm obsessed with quiet units I would choose the following:
NZXT Hale90 750W 80Plus Gold Modular $140 http://www.amazon.com/HALE90-Power-Supply-Modular-HALE9...
Because it has also been positively reviewed many times, as well as other members of the NZXT Hale90 series, as well as other units built on the same platform (Golden Green) by the OEM, Super Flower. These other units include Kingwin Lazer Gold, Lazer Platinum, Sentey Golden Steel Power and Super Flower branded units.
The main cables are as follows:
4+4pin CPU (x2) 75cm
The fan speed on maximum load has been measured at ~900RPM, another review measured it at 700RPM.