[SunkenCiv]

The F-1 engine produced 1.7 million pounds of thrust, and the five-F1 Saturn V put circa 150 tons into orbit. This proposed booster would have five 1.2 million pound thrust engines, and would put over six times as much into orbit. This makes me a little curious, but I'd hazard a guess that the greater payload to orbit comes from dropping the weight of the Saturn V fuel components. (?)

[RightWhale]

So long as the thrust is enough to lift the assembly off the ground, the overall performance will depend on specific impulse. A nuke powerplant would have a lot more specific impulse than the chemical powerplant, which results in much more payload. Specific impulse has units of seconds and is called I_SP or something similar. A way of thinking about I_SP is how long the powerplant can produce that thrust. The chemical rocket will run out of fuel while the nuke will still be blasting away for a lot longer.