In most cases, the UPS will help protect your system from being killed in a power surge/spike. For 1200W your going to pay at least over $500 bucks.
You going to be better off with something like:
APC BR1300LCD 1300VA 780 Watts
I mean come on, your not going to game too long when there's a black out. You can conserve more time on battery just by taking the load off the system, or even perhaps go into standby mode.
Unless your trying to sustain more the 1 PC.
. o O (then just get 2)