R4lNM4N :
Both of these are going to provide enough wattage. Both have the connectors you will need. Though the Seasonic is rated SLIGHTLY higher, the Thermaltake is a single rail PSU and has better reviews from users. The Seasonic will probably work but doesn't claim CF/SLI support. Choose the thermaltake. The Thermaltake is also modular, making cable management much, much easier thus potentially promoting better airflow within your case.
Here's the Tom's link for some good PSU info in case you want to look for something other than that Thermaltake...
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
I wouldn't call Tier 3 vs Tier 3 slightly better. Seasonic makes their own PSU's that are always great, while Thermaltake are made by Channel Well, a company that sometimes makes solid PSU's, but also makes junk. The Seasonic also puts out more wattage. AMD recommends 1000 for CF R9 290, 850 is fine, 775 is cutting it a bit close. And the Seasonic is more efficient, it is Silver, vs Bronze for the Tt.
"CF/SLI support" Is meaningless, the PSU doesn't know what you're running, just has to put out enough power to the cabling it comes with. There are standards for certain connections, ie 6 pin 75w, 8 pin 150w. Its more than puts that out.
Also this is a good explanation on single vs multi rail.
http://www.overclock.net/t/761202/single-rail-vs-multi-rail-explained
A Seasonic over a Thermaltake any day of the week, and the difference between single and multi rail doesn't matter.