Also in regards to performance with projectiles again, just a bit more detailed info on some testing I did:
Check out the video linked for an idea of the performance test I simulated with projectiles. I just did a test of 900 projectiles (the ones shown in the video that fall from the sky, the atom looking ones, which have 3 particle effects on each one) being spawned in almost all at the exact same time, lost about 4-5 frames doing so, but in all thing considered; how likely is it that you will have 900 projectile actors at one time live in your game? If you made a projectile SMG that shot 500 projectiles a second I could see that being an issue, that would be better off with instant hit in that case.
If you make your maps into streamable submaps, you shouldn’t need to worry too much about projectiles impacting things. My logic is; If you can’t see the tree fall, did it really fall? Yeah the sucker fell, despite no one seeing it, but your gfx card didn’t render it because it wasn’t on the same submap 
https://youtu.be/VkPN3cFUI7Y?t=31s
Note: The FPS isn’t amazing due to using a R9 290 currently (limited on budget atm). Also in that video I had motion blur on which doesn’t help the FPS situation. So keep that in mind. Motion blur off I get 40+ fps.
All things considered, you should be a-okay using projectiles for the most part even with intensive PFX on them on multiplayer without much impact. Just be mindful of each gun’s max firing rate when the gun uses projectiles 
As for the line trace w/ PFX:
I haven’t personally tried to use a line trace along with a pfx (yet), but that should be do-able from my understanding of things right now. I’ve seen quite a few games that use line-trace (mostly space flight combat games) along with particle effects. Exactly how it is done, not exactly sure off the top of my head and would need to research it (probably will later today).