Microtek 800VA is not good.They are not true 800VA.I have that UPS its cannot load
C2d e7300,4Gb ram and Gtx560Ti that's why i purchased APC 1.1KVA ups.But the intex 1kva ups costs 1.8k and gives around 20-25mins back to a similar system as of yours in my place. You can ask forum member cilus about it. His friend bought the i5 2400 +6850 combo and has the above ups.
He's kind of totally satisfied with the backup and they've even tested it rigorously. My Vicky's brother in pune has a 955be+msi 6850 cyclone+corsair GS600. He's using a champion 1kva ups and gets 15-20mins of backup even during gameplay.
Although these ups's don't match the quality of APC or even NUMERIC,they get the job done easily and the pricing is really awesome. If you cannot spend more, i suggest the intex 1kva ups @ 1.8k. But don't go below 1kva for these brands. They are not as efficient as APC but does a good job at their pricepoint.