I don't know for sure*. But there's a performance difference at slow speed -- even if their minimum speeds before stall are similar -- a swept-wing jet (any modern jet fighter) at "stall" tends to go into a flat spin, which is a very bad thing and takes time, talent and significant altitude to recover. A prop-powered plane at stall generally just noses over, and given a couple hundred feet of altitude will regain enough airspeed to fly.
A flat spinning jet would be meat on the table for a P51, so there's no advantage for the jet pilot to slow down so much to bring that into a possibility. At the same time, the top speed of a P-51 is about 450mph, which is well within the performance envelope of the F/A-18, so there's no advantage for the P-51 pilot to engage the F/A-18 at high speeds.
Of course this completely ignores either pilot's experience and knowledge of the other aircraft's performance. (I doubt there are more than a handful of pilots who have ever flown both.) It also leaves out modern weapons (missiles) capability. If, as I've heard, a modern missile cannot accurately lock onto the P-51, this becomes a gunfight. If instead, the F/A-18 can lock onto the P-51 at 20 miles, well... Don't bring a gun to a missile fight.
All things considered, I'd RATHER be in the jet.
*As I said, I'm not a pilot. I have taken the controls of a prop plane a couple of times with friends who are pilots. I grew up knowing a couple other pilots who were friends of my Dad. I was a huge plane nerd when I was a kid. I've also put in many hours on MS Flight Simulator which gives you a certain knowledge of aircraft performance. (don't laugh -- you can actually use a several hours on that to count toward your instrumentation time when getting a pilots license.)
I could probably land a small plane without killing anyone, although the landing gear probably wouldn't be pretty afterwards.