According to articles by John Taffin and Ross Seyfried the 500 Linebaugh Long runs 100 to 200 fps slower than the 500 S&W Magnum with the same bullet weights. That's assuming typical guns, which gives the Smith an advantage with the longer barrel. I haven't seen any data from someone shooting a 5" X frame Smith in 500 S&W, but I'd bet velocities would be pretty close to the 500 Linebaugh Long in 5.5" Ruger.
The Linebaughs are going to have more felt recoil though since they're generally chambered in much lighter guns without compensators.