Ok I think it was my "virus" guess that was the issue...
So 2 nights ago after I determined my issue was infection-based considering this has never happened before (even with countless programs open), I ran a full scan of my computer using MalwareBytes. The program picked up 12 Trojan-related applications running on my computer, which effectively was making my whole computer slow down as a result (this is why I thought it was viral in the first place, because my whole computer was slowing down).
After disposing of these issues and rebooting, I gave my computer a rest, and then the next day my ESD pad went nuts and my screen was messed up. So I had to wait until tonight to test out my theory and see whether it was the Trojans that caused all this. So after getting my computer back today I decided to test what Mxy suggested first, then went through a few of my own. The results:
LAN server (no internet): Perfectly fine, consistently around 25-30 fps, ran a few laps around an empty BG map and no framerate hiccups were spotted.
Full BFM server (with xfire open): Same as above, only this time BG was full (I got lucky there considering the variable was consistent ), and my framerate didn't go lower than 22 fps
Full BFM server (with both vent and xfire open): Another small dip, but it never went below 20 fps.
I didn't spend enough time in the server to see if the problem went away completely, but there is a significant improvement. Hopefully I don't have to deal with anymore Trojan applications