I always recommend using the
OuterVision Power Supply Calculator which is also linked to by JonnyGURU (regarded by many as #1 in who's who of PSU testing and reviews)..You'll get a 'recommended minimum' PSU (hover mouse pointer over the results for explanation) and a recommended PSU of higher wattage..There's the
EVGA Power Meter too..You'll get a 10% off discount code (with conditions) in your email towards the purchase of any new EVGA PSU just for using the Power Meter.
Some other PSU manufacturers/vendors that link to, or use, the OuterVision Power Supply Calculator engine on their websites are Antec, Cooler Master, Enermax and Thermaltake.
Is your currently installed 750 G2 'good enough'?..Most likely, yes..Everything works okay, right?..A single +12V rail which the 750 G2 has is what we like, or should.
Would a 750 G2 be a 'recommended' PSU if you were going to buy a new one?..Probably not.
Recommended minimum units may actually use more power than a higher wattage unit (poor efficiency), run hotter and consequently produce more fan noise..See the
Power Supply FAQs at JonnyGURU (Is there such a thing as "too much power"?)..Getting an 'oversized' (wattage-wise) PSU than one that is the minimum recommended is a good move.