I made a test benchmark video in Swiftwater, which I found to always have the lowest FPS, even more than upward.
You will see some dips as low as ~210 FPS on Swiftwater 4th point, and that's without it having all 24 players on it.
Do read the description of the video for some extra details

https://www.youtube.com/watch?v=145Y6LM2m5M

New setup

• CPU i5-13600k
  
• RAM DDR5 2x16 GB @5600MHz (36-36-36-76)
  
• Video Card EVGA GTX 1080 Ti

DxLevel 81 - Mastercomfig Medium-Low Preset

Benchmark1.dem
2639 frames 6.971 seconds 378.54 fps ( 2.64 ms/f) 39.739 fps variability

Benchmark_test.dem
4812 frames 10.726 seconds 448.61 fps ( 2.23 ms/f) 83.439 fps variability

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Old setup

• CPU i7-7700k
  
• RAM DDR4 2x16 GB @3200MHz (16-20-20-38)
  
• Video Card EVGA GTX 1080 Ti

DxLevel 81 - Mastercomfig Medium-Low Preset

Benchmark1.dem
2639 frames 11.861 seconds 222.49 fps ( 4.49 ms/f) 19.482 fps variability

Benchmark_test.dem
4812 frames 18.558 seconds 259.30 fps ( 3.86 ms/f) 38.363 fps variability

Very happy with the results. About 70% increase in average fps!
I use a 240Hz monitor, and with the 7700k, the frames would dip way below that quite often.
However with the 13600k now, I'd say 90% of the time I'm over 240 fps

Since you are using custom crosshairs, the files used to set the crosshair for each weapon is the same file used to change the explosion effect. So what you need to do is change the following files in your custom crosshair folder:

tf_weapon_cannon.txt
tf_weapon_grenadelauncher.txt
tf_weapon_pipebomblauncher.txt
tf_weapon_rocketlauncher.txt
tf_weapon_rocketlauncher_directhit.txt
tf_weapon_rocketlauncher_airstrike.txt

Go into each of these files and change "ExplosionEffect" and "ExplosionPlayerEffect" to this:
"ExplosionEffect" "muzzle_minigun_starflash01"
"ExplosionPlayerEffect" "muzzle_minigun_starflash01"

And you should be good to go my friend

From my findings you need to do the following:
After launching TF2:
1. Create a custom server with any map, so type "map ctf_turbine" in console
2. Join as the class you use this mod for and switch your weapons around (as in switch from primary to secondary and so on..)
You need to do this for every single class you have this mod used for. So in my case I have this mod used for sniper and spy, so I join the server, go spy, switch weapons around, switch class to sniper, switch weapons around.
If I only do this for spy, then spy is the only class this mod would work for in Casual. So you need to do this for the class you will play as in Casual next, however many.
3. Exit the server
4. Queue for Casual.

Now the mod should be working in Casual with no issues, and re-queuing should not cause any issues.
You need to do this once, every time you start TF2
Let me know if it works for you or not.

This mod stopped working properly on Casual mode as of today, August-27-2020, after an update was released for the game.

The note says:
"Fixed bsp-embedded models caching rules to allow for reloading the correct model when transitioning to a different map"
I think the mentioned fix note is the cause. Here is what I noticed:
The mod does not work when joining Casual upon launching TF2 (with the correct use of preload_room).
The mod DOES still work in Casual (temporarily) if you join your own map before joining Casual.

So after launching TF2, I type in console "map pl_borneo", which puts me in a borneo game where the mod works perfectly on, and then I queue for Casual. The mod works as expected when joining a Casual match after doing so, BUT if the server restarts or if I join another Casual match, the mod stops working and I have to disconnect, create my own game ("map pl_borneo"), and then queue again for Casual.

So it's the changing of servers or restarting a server that causes this mod to stop working.
Hopefully it's an easy fix, because I absolutely love this mod and have been using it for years.