800VA UPS for a 500W PSU

[immortalgamer]

Recently, there have been a lot of power outages in my area. I've decided to invest in a UPS so I can safely turn the computer off and prevent the hard disks from failing.

Here are the PC specs(nothing is overclocked):

AMD Phenom II X4 965 BE
6GB RAM
Sapphire HD 6850
2 Seagate 1TB 7200

I use a Cooler Master 500W PSU with 70% efficiency.

I'm pretty sure a 800VA UPS will be fine if the computer is on idle or during tasks like surfing etc. but can the UPS supply enough power when the computer is on load?
Also, how much backup time would I get from this UPS?

Thanks.

 

[helpstar]

https://www.apc.com/resource/include/techspec_index.cfm?base_sku=BR800I

Look at the diagram on this site, it's just for this UPS, others could be different but at least 5 minutes with this one under full load.