Wow CPU bottleneck is WAY over rated, Unless the game is CPU limited you will almost always get better performace by getting a better GPU. Heck you could probably go up to a 7970/680 basically however you would just get diminishing returns depending on the game and resolution.
My system is very low powered(anything that can be undervolted is and anything that saves power has been done), so if i game on it, most of the time the peak would be about 150 watts. it idles under 40 watts and runs folding @ home on the cpu @ about 90 watts.
Not all systems are this low powered, but to be honest, I have a hard time pulling 350 from the wall on my main system.
When you look at power supplies for modern systems, You want high 12 volt current(wattage divided by voltage = amperage).
Your power supply has 46 amps @ 12 volts. so it has lots of power any single video(and single gpu) card system.
What you have to watch out for are cheap power supplies that have a 450 watt label and only deliver 180 watts @ 12 volts.
While the 5(usb/parts of hard drives/ssds/ect) and 3.3 volt rails are still used, but not as much as the 12 volt rail(cpu/video cards/ect).
Most modern power supplies even those with multiple 12 volt rails just have one large 12 volt rail and then split it with current limiters(these prevent more then lets say 20 amps from passing, it was put in as a safety when high capacity power supplies started to be popular. Some still use it others do not). This same rail is also used to feed the 3.3/5 volt lines by use of something called dc-dc conversion(its a small power supply that takes 12 volts and makes 5 volts or 3.3 volts.). because of this, you will notice that most power supplies seem to have MORE wattage then is possible by numbers alone(but as long as the TOTAL does not exceed any of the limits it all works well.).
This is a 300 watt power supply with 24 amps on 2 12 volt rails, As you can see, adding the 2 rails would not work(17+17), but the 288 watts / 12 gives the MAX 12 volt amperage(24). You will also notice what I mention above about being "more" then 300 watts listed, but as long as ALL rails stay within the limits set and the total of all do not pass 300, all is good. Please note that high 3.3/5 volt usage will take some away from the 12 volt rail to keep the combined(300 watt max) within check(so take 100 watts of the 3.3/5 volt rails WILL take that much from the 12 volt rails). Lucky for us, it is almost never a problem for the end user.
One more thing to know. You may see lots of people saying that 80+ power supplies put out more power. This is NOT true. 80+ power supplies waste less power to make the same amount of power. If a power supply is rated for 300 watts, It is 300 watts DC(12/5/3.3/5vsb/ect) NOT the amount of power it uses. So a 300 watt power supply can pull more then 300 watts from the wall if fully loaded. The amount more depends on the power supply efficiency(80+ power supplies will almost always pull less power from the wall for the same amount of DC power being put out, but if both are rated the same, they can put out just as much power). This said, 80+ power supplies are newer designs(they run cooler because they waste less power) and generally designed better(more 12 volt power. The DC to DC thing helps efficiency).
It is allot of info, but I hope it helps the computer power supply seem a bit less hard to understand