Those seem to be newegg prices so I'm assuming you're in the U.S. Those CX and RM units are overpriced. You can get better quality units for less in each efficiency and capacity class.
You don't need as many connectors as in 1000HX which had six PCIe connectors. if I'm not mistaken, your graphics cards use three PCIe connectors in total. Even many 650W units have four PCIe connectors.
I would buy one of these at the moment:
XFX 750W XXX Gold $105 ($85 AR) @ NCIX
It's a copy of Seasonic X750 which is better than Corsair RM750. See reviews by JonnyGuru:
Seasonic X750,
Corsair RM650,
Corsair RM850. Also, review by the XFX 750W XXX itself by
hardwaresecrets.
Rosewill Capstone 750W $100 @ Amazon
A fine choice as well, it's an all-round high performance unit that also uses better capacitors than RM series. 7 year warranty.
I'm thinking of going with Corsair again as I'm assuming the connectors would be the same (please correct me if I am mistaken).
The types of connectors used are the same across all units, just the number of each type differs. The number of connectors mostly depends on how powerful the unit is, but there are some differences between brands as well. But buying a Corsair unit doesn't mean it will have the same number of connectors as another Corsair unit, even if they had the same labeled wattage. Usually equally powerful models within the same brand have some minor differences in connectors.
The CX750 is "Bronze" certified, the other two are "Gold" certified. Does anyone know what the difference between Bronze and Gold is?
It refers to efficiency, that is, the percentage of AC intake watts that turn into DC watts for the components. The higher this number, the less waste heat is produced by the PSU. This can increase the lifetime of its internal components. High efficiency also means the PC uses less electricity, which affects your electricity bill. 80+ Bronze efficiency is roughly between 82-87% (depending on the particular unit and the load) in the North American 120V network. 80+ Gold efficiency is about 87-90%.
In a PC consuming as much power as yours, and with an average cost of electricity, you'll save a few dollars per year going with a Gold unit instead of Bronze. If you leave the PC on 24/7 and/or have relatively high cost of electricity, a Gold unit might pay itself back as an investment compared to buying a Bronze unit.
A common misconception is to think of 80+ ratings as some sort of quality ratings. You
can think of efficiency as being a part of quality but what really matters for quality is reliability, and efficiency doesn't directly imply reliability. A highly efficient unit can be unreliable and a not so efficient unit can be extremely reliable. It's just coincidental that often highly efficient units are also reliable since high efficiency is costly to manufacture, so customers expect the units to actually perform well too.
Also, is the RM 850 a significantly better unit than the RM 750? Other than the wattage, are they essentially the same?
Wattage is most likely the only difference.