The biggest you can find. Those CRTs often draw as much power as the PC it's attached to.
As to 900 Watts that would be 300 Watts apiece and right at the edge. To truly answer this you would use a P3 Watt Meter for about 20 bucks to see what the peak power draw is.
In fact my bet is that by ejecting the old CRT you can save some Watts and for the cost of the 15 inch LCD you can save that much on the UPS!
Laptops already have their own UPS. Why add another?
Bob
I service computers and want to buy a UPS. I will have 2 power strips plugged in. These are the most devices that will be running at one time off UPS power, (worst case scenario)

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