As far as power supplies go Thermaltake ranges from crap to mediocre. Certainly not something to buy unless they are all you have access to. Even more especially when it's priced higher than the best models on the market.
What will you be running that requires 750 watts? At least 2 x GTX 670s or 2 x HD7950s/HD 7970s. With a high end system like that get a Seasonic X 750. Among the best power supplies made.http://www.newegg.com/Product/Product.aspx?Item=N82E16817151087
No power supplies are going to be super efficient at truly low loads like that but the difference is small.