Wish I had seen this earlier. I have two SmartUPS 1500RM2Us in my network. These provide longer run-time than the consumer 1500s AND have true sine wave output, which is often easier on electronics and does not cause the physical resonance you may hear in a lot of electronic equipment like my audio receivers, TV, and projector.
Anyway, I get about two and a-half hours run time from each having split the system between network equipment, DSL modems, internal server (AMD K6-3+/450,) two NASes, and a Core-i7 HyperV machine. I have paired them both with an APC MasterSwitch which I have programmed to cut devices as the power decreases depending upon need.
The Hyper-V machine shuts down almost immediately and takes its NAS with it as it is just a testing and template system. The second NAS shuts down when it detects either its directly connected UPS or my desktop UPS has started shutting down, as it hosts an iSCSI LUN for the desktop.
At a point of a power outage I wind up with nothing more than the internal server, primary network switch, and the wireless firewall with VDSL running. I have plotted to move the power equipment and the internal server up to the firewall so I can squeeze a little more run-time by killing the primary switch, but it draws a near negligible amount of power.
During the last hurricane I connect my fridge to a consumer 1350 and it run the fridge for three hours. Of course, while powering the fridge it registers about 44 minutes run-time, but even that is far less than the expected draw based upon the rating placard in the fridge.
I have a SmartUPS 1500 (SUA1500, tower unit) on my entertainment system and with the Intel NUC, the OTA digital DVR, the 3200 lumen projector, and the Onkyo receiver it will run a little over two hours (about 166 minutes, give or take.)
A lot of gobble there just to say, yes, you can get some amazing run-time for even a well outfitted system. While I prefer to use SmartUPSes for the true sine wave output, they are more expensive and YMMV. I just do not like running stepped-approximation power through my electronics... it makes me feel uneasy.