Do you think this PSU will be enough?

I got the same psu u want and a gtx 660 with an core i5 and your gpu only takes 5+ watts than mine.

500w should be plenty. IIRC the 970 only uses 125 or 150 watts on load.

Try one of these:
http://support.asus.com/PowerSupply.aspx?SLanguage=en
or
http://www.extreme.outervision.com/psucalculatorlite.jsp

Just my two cents here but if your going for a psu upgrade wouldnt it be better to skip going up 50w and get something with a significant power difference? i know the wattage is not the problem but the difference between a 550 and a 750w psu is like £20-30.

Nobody posted "500 WAT" picture? SHAME!

Um, you're buying a PSU rated for 50 more watts? If you're going to buy a new PSU because you fear that your current generic doesn't have enough juice, then actually exceed it by a substantial margin.

Can anyone tell me how do people decide what PSU to buy? How much is too much, or too little? Do you use one of those power supply calculators?

That should be plenty TBreaker, and it's not a bad PSU to boot. Tier 2 Class A. Highly recommended for those wanting a solid PSU on a budget.

I don't know what your generic one is, but a PSU is quite important! Buy a good quality one, the cheaper ones tend to degrade quicker and provide less stable current which increases the wear on your components slightly.

the XFX Pro Series are really good PSU, with lots of japanese components, and 550W is enough for your PC, obiusly Sli is a far cry for that PSU.

500W - 550W should be enough. But i strongly recommend not to save on PSU, this can looks not very important, but it's the most important thing in your PC - it's the power, if you will take cheap one, it could ruin whole your system.
Personally i recommend to put all your greediness away, find a litle more money and take something like Seasonic X-series with 80+ Gold efficiency, or something similar.

50W may seem insignificant however if you are switching from unbranded PSU to high quality brand it makes sense. Also no point in buying anything higher than 550W, you are getting the best performance for the buck with around 80% load as far as I know so having an overkill PSU is just a big waste.

Also congratulations on your new PSU, would love 970 myself but it is too expensive for me atm so I will probably grab 960 which is to come out Q1 2015 if it is any good.

w,e PSU you get, make sure its a gold or platinum rated.