A PSU is most efficient at 50% load, even then some of its output will be lost to heat. 80+ Gold means the PSU is rated for 80%+ efficiency, and Gold should be around 87% efficient at least, so that would mean a 750W Gold PSU can support up to ~652W of actual consumption. In a stock system - no overclocking, messing with power limits - the 750W recommendation will work. Just realize you don't have a lot of headroom if any.
I'd personally recommend looking for at least a 1000W PSU if building a new system with high end GPUs and CPUs in mind today... but keeping in mind the 50% is the sweet spot, 1200-1300W PSUs might be closer to the mark for ultimate efficiency. Pick a single rail PSU over multi rail.