and there are shockwaves or beams firing off, I get massive slowdowns
It's normal for the Super-High-End Shockwaves (Texture: 85 MB+), are you using that, I recommend you use Normal or High-End Shockwaves, it doesn't matter the overall of your PC, Super-High-End Shockwaves drop always the FPS to 4 or so in D3D 8 Mode, in OpenGL it works OK, there is no slowdown if your PC can manage it....
For the Beams, it could be the Muzzle Glow, you must be using the Animated Beam Glow, that uses about 12 MB, it can slowdown your game if your PC doesn't really meet the requeriments to manage it........
There is a Muzzle-Beam-Fix, which changes the Tables so no Animated Beam Glow, that use less memory.......I can give you the Link to the TBL, but probabily the Weapon.TBL maybe it's not updated to be used with the MV v3.6.8 Delta......
I would tell you the requeriments, but my machine don't really suffer any slowdown because of Bitmaps and Textures, so.....
What's your PC Specification ??? (Hardware and O.S.)