Nice mission mate !
I flew it twice cause at first time I was shot down...
As I said, I used the P-51 with guns & rockets. I really had a good
time killing the bandits ! And the overall feeling of the mission was
of a good combat sortie... with both moving & static targets.

I would suggest make it default for native FSX P-51 (provide also files for F-86)
and upload it to CS Weapon Liveries as an addon for this...

Now just for discussion's sake :
- In my missions, if player has been hit, I use sound file of bullets striking the plane,
or even a cry "nuts ! I've been hit !" and as a failure, I preffere "engine fire", so that
player can see a visual effect of being hit...
- I had also the idea (recently) to make a second livery with some bullet holes & scratches
over plane's starting livery & after player has been hit, mission to perform an action of type
"change user aircraft to" the damaged livery plane (added in Aircraft.cfg also of course)...
But I have not tested this idea yet...  ;)
- About the FPS impact at target area : I think not much can be done due to many "aircraft"
type vehicles, though you didn't over do it ! Good machines will have no special problem
with your mission.  

As a conclusion, as I have already said, this addon (CS Weapon), reveals it's full potential in
FSX Missions. It's a pitty that we don't have more mission makers with this interest...