I've got a system comparable to that running fine on a 750w PSU. So not sure what they're talking about. I tend to use: http://extreme.outervision.com/psucalculator.jsp when I need to figure out approximate usage rates. So far it's been spot on for me.
But as I said before, I've got a system with a few more drives than that running fine on 750w. (Think I was at like 607w iirc)
2 GTX 560 Ti's in SLI won't push your total load over about 600 W even with some OCing so the Seasonic X760 will be plenty, its a good unit that can handle that system with ease, i would take it over a cheap 1kW unit anyday.
Also, most people in the store have no idea what they are talking about sadly, or they may be recommending a larger unit because they run on commission or their 1 kW units are kinda crappy and only keep up with good 850 W units.
The Seasonic X760 has 4 6+2 connectors to go to the graphics cards(they will work as 6 pin or 8 pin PCI-E connectors), no other components need those PCI-E connectors so you are fine and will not need to use any adapters. Most 750 W units and bigger have at least 4 PCI-E connectors and are capable of running 2 560 Ti's.
You will have plenty of connectors for the system, its got plenty of SATA and peripheral connectors for pretty much any system so you shouldn't have any issues with that unit and your selected system.
Nope, the PCI-e slot itself is capable of providing up to 75 W which is plenty for most cards, would provide the power to the sound card, at most it might need a peripheral/molex connector. The 6 and 8 pin PCI-e connectors are really only for power hungry graphics cards.
Fans, pumps, lights, and other items in the system connect to a peripheral connector for their power, your hard drives and optical drives will connect to SATA power connectors, you have 8 SATA and 8 peripheral connectors on that unit.
If you're not OCing, I'd get the 750 watter to handle SLI..... if OCing get an 850 watter.
You will need two 6 pin PCI-E connectors per card.
In the 500R, I'd recommend the HX850 (10.0 jonnyguru performance rating), TX850 V2 (9.5 jonnyguru performance rating) or XFX Core Edition 850 (9.5 jonnyguru performance rating).
I'd move from the MSI to the Asus model of that card though. If you gonna be doing heavy OC'ing the MSI prolly has just as good a cooler but the VRM is a bit lacking....it's 6 phase VRM design doesn't stack up to the 7 phase design of the Asus.
I have installed 11 of them so far (4 SLI builds, 3 single builds) (and all but one managed 1000MHz w/o a voltage tweak.
Note that it's not just about staying under the unit's max voltage and not blowing the box up....it's also about maintaining stable voltages, low temps and low noise as you gear up to maximum load. A bit of headroom means.....
1. PSU runs at greater efficiency .... PSU's hit peak efficiency at 50% load.
2. At lower % of full load, temps are lower and fan speed (and noise) are lower.
3. At lower % of full load, less strain on PSU and therefore voltage stability is more uniform....varying voltages is the enemy of a high OC.
All 7 of the above builds have 850 watters in them (most are CP-850's, few HX850) ..... all are dead silent @ conservative OC's of 4.6 or better GHz on the CPU and 980 - 1020 MHZ on the GPU's.
Here is what EVGA recommends for their graphics cards:
GTX550ti needs 400w with 24a on the 12v rails plus one 6-pin PCI-E power lead.
GTX560 needs 450w with 24a on the 12v rails plus two 6-pin PCI-E power leads.
GTX560Ti needs 500w with 30a on the 12v rails plus two 6-pin PCI-E power leads.
GTX570 needs 550w with 38a on the 12v rails plus two 6-pin PCI-E power leads.
GTX580 needs 600w with 42a on the 12v rails plus one 6-pin and one 8-pin PCI-E power lead.
GTX590 needs 700w with 50a on the 12v rails plus two 8-pin PCI-E power leads or 4 6-pin power leads.
That will include allowance for a normal complement of drives, fans, etc. Most of the power draw comes from the graphics configuration.
In your case, a second GTX560ti will need power from the slot, and two 6 pin power connectors. Each can deliver 75w for a total of 225w extra over the 500w base amount.
In actuality, you will never draw the maximum. Any psu will have enough of the other type ov connectors for hard drives, fans, etc.
You really need only a quality 750w unit, although it is never really wrong to overprovision the psu a bit.
Seasonic is a top quality psu, and will deliver it's advertised power and more. I think you are good with the 760w unit.
But, also look at PC P&C which seems to be having deals now, along with Antec, XFX, and Corsair. I would not pay much extra for a modular psu unless it needed to fit in a very small form factor case. Cable management neatness counts, but it is not that hard to do. You will find that you will be using most of the supplied power leads anyway.
However, I can get the HX 850 at roughly 30 dollars more and the CP-850 at about 80 dollars, would it be better if I got them instead so I could OC if I decided to in the future ? You also didn't recommend the CP-850 despite using it for numerous builds, is it not optimal for the 500R ?
What is the difference between the TOP version and the non-TOP version of the ASUS card ?
The TOP one seems to be cheaper.
In terms of temperature and fan noise, which of the listed cards is more superior ? If could get both cards at the same price.
The CP-850 and CP-1000 are custom form factor units that only work in select antec cases, they are much bigger which lets them space out the insides more and make it for less, but they won't fit in any non-antec cases.