Another useful pdf that discusses various issues for Orion style systems in detail
Here is a paper from 1964
Thanks to from the writer Mauk2 on the nasaspaceflight forums The forum has a lengthy discussion on all things nuclear pulsed propulsion.
Mauk2 has an interesting speculation about using the planned Ares V and some SRBs to loft 600 tons of a pulsed propulsion vehicle about the turbopause
From the first pdf, Table 1 on page 16 has a column labeled "W, m/sec." W is the parameter assigned to the specific strength of the pusher plate material.
The W parameter is very, very important in the performance of an EPP using plasma drive. In 1970 they assigned W a value of 300 meters/second, which was the performance achieveable with steel at a density of 8 grams per cubic centimeter and a yield strength of 100,000 pounds per square inch.
Using modern steel (strength of 500,000 psi), the W parameter goes from 300 to 600 or better. This one simple improvement would result in an Isp of 10,279 seconds in vacuum. Hold all other parameters constant, and merely scale them by a factor of six to cover the larger mass of this design versus the reference 100 ton design. Instead of 20 kilograms, the pulse units mass 120 kilograms. If the total launch mass is 600 tons, 108 tons in propellants and 192 tons in structure, payload would be 300 tons. It would be one stage to Mars.
Making the pusher plate out of stronger and lighter materials would further improve system performance.