GPU needs 60W, CPU needs 65W. Peak load of that puts it just around 150W factoring in the board and drive. Figure this means a 250-300W PSU.
A 600VA UPS can run 200W for ~8 min while a 900VA can run 200W for ~14 min. The 600VA can handle 300W for 3 min, and the 900VA can handle 400W for 3 min. Odds are you'll be present if the system loses power while at full load, and if you're not present then it is nearly idle. Plus these things have software to automatically shut down once the battery is drained to a certain level.