In the past few patches or so I have been experiencing pretty bad FPS drops to the point of making the game almost unplayable. I start the game around 60 FPS and randomly even when sitting in the pool it will drop to 10-12 or even less. Even a few months ago this never happened when I was playing at higher graphics settings. I now have everything turned down to the lowest setting and this problem still persists. Like I said though this seems to be completely random. It will drop for a minute or two then go back to around 50-60 fps.
I have a Dell Latitude E6400. Windows XP 32-bit, 4 GB Ram, two 2.26 ghz core 2 duo processors, and an Nvidia quadro nvs 160m.
While experiencing this lag my computer is operating within normal temperature ranges. Around 50*C for the GPU and CPU and 60* for the chipset. Also I have checked my CPU usage while playing a game even during team fights it remains at about 60% usage.
To fix this I have tried a fresh install of HON deleting all folders before reinstalling. I have double checked my graphics setting to make sure they were in performance mode. I lowered pretty much every graphics setting in the game. I changed the priority of HON to high. OpenGL doesn't seem to help at all. ]
Prior to your Nvidia rollback, did you update your graphics card to see if it resolved the issue? Also, did you also reinstall your graphics card?
What is your remaining RAM prior to opening HoN? In lobby? In 5v5/3v3 game once on the actual map/game (no-stats if you wish to test)? (Basically, free up as much RAM as possible, especially if your computer is using virtual paging while HoN is active).
Disable your sound. If it works, update/reinstall your sound cards.