Enermax is just a better brand.
PSU brands matter very much. One brand isn't just as good as another one.
The worse brands tend to use fewer and lower quality parts than the better ones, which means they usually die faster, put your other parts in more danger, and they often have less protection against catastrophes than the better brands do.
I haven't investigated the PSU you chose and the closest Enermax alternative, but even so I would put money down on the Enermax being higher quality on the inside.
My guesstimate, you would probably get an extra year or two out of the Enermax before its time to get a new PSU.
That being said, the 1000w does sound extremely high. Usually it takes 2x high end video cards that are OCd or 3x+ non-OCd video cards to get into that range.
I haven't heard too much about the Quadro 4000, but I looked up a spec sheet that said it uses a maximum of 152w here
http://www3.pny.com/NVIDIA-Quadro-4000-P2903C365.aspx
this link says it needs 1x 6 pin here
http://www3.pny.com/support/media/Files/4bde3cc7-7f8a-4898-ad03-42fbcc1b4082/Quadro%204000%20Additional%20Power%20Requirements%207-19-10_v1_v1.pdf
which has a maximum safe draw of 75w from a 6 pin pcie connector + 75w from the motherboard slot which totals up to 150w or very nearly the 152w from above.
You can OC beyond that, but per the official power supply mechanical specifications it is not a good idea.
If the computer is only going to have ~150w of video card draw, I can't see the full system getting up to 1000w even with 2x Xeon processors at the same time if you ever get the second one.
Un-OCd the Xeon processors will use 80w of power each so call that another 160 for 300w total.
Outside those two things most systems don't reach another 100w of combined load, call it 150 to be safe.
That is about 450w.
For the sake of argument you might throw another graphics card in there or do some medium OCing so add maybe 300w for that and you can probably get by with a high quality 750w like this one
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207015
Again, I don't really claim to know how you intend to use the system, but that is just a rough estimate meant to be a little conservative.
If you intend to go for heavy OCing, to get another video card and another processor and do light OCing, or to add multiple more of these video cards even with no OCing then the 750w will probably not be a conservative estimate anymore.
As far as multi-rail goes, it is a pretty mixed bag. Single rail setups don't have as many configuration problems, but the tradeoff is that the protections kick in at higher wattages than multi-rail setups so your parts are in more danger from things like power surges.
Multi-rail setups are the opposite, they can be harder to configure when you are trying to balance the loads across multiple rails equally, but the protections kick in at lower wattages so it is more easily able to shut itself down to prevent a power surge getting through to the motherboard or video card, for instance.
If you have a Surge Protector you will be plugging everything into, that kinda takes up some of the slack in this regard and lets you more safely go with a single rail setup like XFX uses.
I would suggest everyone put their computer into a surge supressor regardless how many rails they have, though, and that doesn't mean there is no value in multi-rail.
TBH, I wouldn't worry too much about the number of rails. I would just focus on getting a solid brand with as many watts as you need and accept the number of rails that you end up with.
Going back to brands from before and how I said they do matter a lot. Here is a review of a 750w Thermaltake PSU
http://www.hardwaresecrets.com/article/Thermaltake-TR2-RX-750-W-Power-Supply-Review/902/7
that succeeds delivering 60% of stated wattage, but fails at 80% of stated wattage and which provides the worst ripple charts that I have ever seen. Indeed, they are far outside the technical specifications on the most important rails (the 12vs).
Here is one from the XFX 750w that shows it can do 100% of stated wattage with beautiful ripple charts on the 12v
http://www.hardwaresecrets.com/article/XFX-PRO-750-W-Power-Supply-Review/1182/7
and on the next page
http://www.hardwaresecrets.com/article/XFX-PRO-750-W-Power-Supply-Review/1182/8
it says the tester was able to get up to 912w out of the XFX 750w.
The last pass within specifications on the Thermaltake was at 440w and the XFX last pass within specifications was at 912w, that's almost a 500w difference between the two PSUs that are rated at the same wattage.
- edit - BTW, the XFX 750w Black Edition PSU does say that it has 1x 8 pin EPS 12v and an additional 4 + 4 ATX/EPS 12v connector, so it should be able to power everything if my wattage estimates from above are somewhat realistic of how you intend to use the PC.
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