As far as I know the iSP (specific impulse) of Orion is a lot higher, which may result in better overall performance.
There are some high temperature nuclear rocket engine designs though, like nuclear gas core rockets. They're crazy reactor designs you would never try running down here inside a biosphere but have energy densities far higher than anything else save a bomb.
There are some high temperature nuclear rocket engine designs though, like nuclear gas core rockets. They're crazy reactor designs you would never try running down here inside a biosphere but have energy densities far higher than anything else save a bomb.