About my ups

It all depends on how much lower. Generally, no PC draws the full rated wattage from the PSU. Therefore, the UPS is rated slightly lower than the wattage of the PSU; say about 80%. And don't forget to add in the monitor load.
 
for example,

i have a 1000watt psu but typically my draw is no more than around 300-450watts total (for my tv + pc). i'm using an APC 865watt backup which gives me about 7-9 minutes runtime in case of an outtage. this is more than enough for me to save files and shutdown the system but not enough to keep working for an extended period of time.

looks like i fit in around ubrales 80% suggestion.