Guys I've found a solution. Thanks everyone for posting/upvoting etc.
It was my projectile sapper particles that were causing the lag. That's why I noticed the issue more on soldier though on scout when sent airborne (BY A PROJECTILE) the issue persisted. The game runs fine now; this has been bugging me for ages!
For reference:
"ExplosionEffect" "ExplosionCore_sapperdestroyed"
"ExplosionPlayerEffect" "ExplosionCore_sapperdestroyed"
"ExplosionWaterEffect" "ExplosionCore_sapperdestroyed"