Sorry its more of trade with a friend so i have to choose between one of those two actually.Personally I wouldn't get either of them. At the moment for just £3 more than the CX750F (OCUK prices) you can get a gold rated, fully modular Seasonic GX-750 with a 10 year warranty and is a much better psu than those two.
Still the Corsair. If the Thermaltake is still sealed in it's box are you sure you posted the correct model because from what I can find the Toughpower XT 875w launched over 12 years ago, was never updated and has been end of life for several years? Their newer models such as the Toughpower Grand/GF1/GF2 are all 850w and usually have RGB.