I cannot stress any more than I already have that I don't trust this PSU.
It is extremely easy for a PSU to get good reviews especially from people who have no idea what they are talking about.
That being said, this particular exact model has pretty much nothing but bad comments on Amazon. See here:
http://www.amazon.com/Thermaltake-RX-850-W0319RU-Modular-Management/dp/B001QXDQB0
Here is an example for that exact model
This PSU is an ultimate fail. Mine went out after 7 months, filling up the room with Smoke. After inspection, I noticed that an unused PCI-E power had melted down. The PSU was connected to a simple computer build (blue ray drive, 1 hdd, no video card) but was purchased for future expansion hard drive expansion.
Here is another one
I bought this product for use with a Asus Super Computer motherboard. MB kept dieing. Took it in for replacement, turned out it had thermal damage. Took it to be repaired, damage to my $600 MB was because of THIS PSU! Repair people told me one of the rails was not putting out the correct voltage because of a product defect and this was becoming common place with Thermaltake. Thermaltake $100 in repairs and long days and nights of heartache and have made my personal black list. Hello Corsair ... are you gonna stay good?
It isn't just about stated wattage, it is about the "cleanliness" of the delivery.
This is what ripple charts are supposed to look like, from my PSU:
http://www.hardwaresecrets.com/article/XFX-PRO-650-W-Power-Supply-Review/1165/7
Mind you, this isn't "ideal", but it is extremely good. Ideal would be the 12v rails with charts that look like the +5v and the +3.3v charts.
The ones shown for the 12vs are almost always wider than the +5 and +3.3s because power makers can vary up to 5% on the 12vs so potentially a 12v should be at the worst putting out juice in the range of 11.4 - 12.6 to remain in spec, but the one I showed was tighter than that, at about 11.7 to 12.3.
The closer you are to a consistent 12, the less your parts are likely to blow up.
Here is a review for a Thermaltake TR2 RX branded PSU, nearly the same with what you selected (750 vs 850)
http://www.hardwaresecrets.com/article/Thermaltake-TR2-RX-750-W-Power-Supply-Review/902/7
If you notice, it has FAIL written all over it.
The highest test with PASS written on it was for 440w which was 58.8% of max load. Everything above that failed miserably on the 750w Thermaltake PSU.
If you are going by this standard, you can't trust the 850 for any more than about 505w.
Additionally, and this is extremely important, look down at the ripple charts I mentioned before that showed the XFX giving out 11.7 - 12.3
On this Thermaltake TR2 RX 750w, the variance is actually off of the charts. The +5v on this PSU looks like the XFXs +12v. The +12v charts shown here are an example of the absolute worst possible chart that you can possibly have, bar none. There is no possible chart that can be drawn that is worse than these 12v charts.
With charts like those, you are maximally likely to destroy things like your graphics card and motherboard for every minute of usage.
It may take many minutes of that usage, even years worth, but you are rolling the dice the entire time.
I will not under any circumstances reassure you that your PSU will work safely and protect your parts from damage.