The gauntlets of Atlas multiply strength by x10 (they don't bump you up to Atlas's level if you're not already pretty strong, but in the hands of someone with significant strength can boost above that level).
The sandals, on the other hand, aren't a multiplier but provide a more set boost. How much specifically I'm not sure, but at least it allows supersonic speeds, minimum (it doesn't automatically grant skill at using that speed though, practice is needed to be really good with it), as well as flight. Both Wonder Girl-Cassie and Queen Hippolyta have used them to grant speed and flight in the past.