Thermaltake Smart 750m vs Corsair AX760(Mid-end vs High-end)

Hi, I'm planning to buy a new PSU for my graphics Gtx 970 and thinkin in futureproof planning to add another Gtx 970 for SLI, one SSD and some basic overclocking(gpu & cpu).

I saw a lot of reviews of the thermaltake smart series including of "Hardoc" and looks like a good product, passes the reviews, deliver the wattage it claims and survive the test to 100% load.

My question is if i would get a real benefit(apart from energy saving) for get the Corsair AX760

to sum up: why a High-End PSU is better than a Mainstream(mid-range) PSU?

in addition the thermaltake is much cheaper and I can buy directly(the corsair have to wait 1 month)

Thankz in advance for the help

Thermaltake Smart 750m vs Corsair AX760(Mid-end vs High-end)