You don't need 750w. 550w will be plenty, including any OC you can use.
And the njoy are junk. 51A (612w) on 12v rail, group regulated and sharing 3.3/5v+ rails (16A/14A, combined 122w) for a total of 734w. For a 750w psu?
By comparison, the Corsair RMx 750w has 25A/25A (150w) on 3.3v/5v+ rails and 62.5A (750w) on 12v rail and almost every protection there is for an ATX psu.
The njoy psus are basically a 10+ year old really cheap design with a fresh coat of paint.
The psu is the single most important component in any pc. It has direct voltage ties to everything. If you needed a new heart, if given the choice would you really get the new heart from a 90yr old alcoholic chain smoker just because it's a few € cheaper?