I did the regedit tweaking with my laptop with a match and in my case, the FPS issue seem to kick in way faster than expected *2 minutes mark*. After reverting back to the original values after a few restarts, the issue seem to be gone already with the number of matches I've played today.

I'll try the monitor logs as Brent has suggested and I'll post my results hopefully by tomorrow.

Here are the r3d logs I've had for the matches without the issue as of today:
1st log is a match at custom with fully loaded bots.
While 3-4 are normals.
5th one is with the registry tweak.

*max settings (40-60 fps) without any other proggies running in the background*

I've had problems with FPS for awhile now, but it was REALLY bad a few nights ago, to the point where I had to dc and reconnect so I could see half of what was going on. I hope these help!

everyone should thank this red, searsly it's the first time i saw one actually working =P
btw, after sejuani patch i have ridicules LAG during all match, but i'll remake my pc tomorrow it should fix if not i'll come back here later ~

Just played another game, here is the log. Final verdict on the registry work around is that it only kinda works. For me it moves the drop later in the match, for others, sooner.

http://www.mediafire.com/?6rbxbfi66iq49cz

The big drop happens around 49 minutes into recording (scroll down to 4:49:03.237), and seems to coincide with a large PATH NOT FOUND rads error. There are of course several other overflows:

4:51:07.2790575 PM League of Legends.exe 3076 RegOpenKey HKLM\SOFTWARE\Wow6432Node\Microsoft\CTF\KnownClass es NAME NOT FOUND Desired Access: Read

This one in particular crops up half a dozen times. Take a look, and THANK YOU for getting into this problem brentmiester.

ERROR| Assert Description: General hard assert occurred, game may crash!
ERROR| Assertion failed!

Does this have anything to do with the crashes? And are you going to fix it if so?

I didnt' post my files the first time I spoke here because I was SOOO happy that I was being able to play without the FPS drops (by deatcivating my antivirus/firewall and the in-game sounds) that I ended up playing lots of matches with a somewhat regular rate of 40-59 fps (but almost never reaching 60, either stoppig at 59 or sometimes going to 62 and dropping again). Those following matches have all been played with both antivirus/firewall and in-game sounds turned on like normal, and yes they did had several FPS "chokes" on several times during the matches.

I did send a ticket to chewbacca a couple months ago and he helped checking some stuff in my PC (up till the antivirus that I'm still waiting to do so I can get back to him...) and my old logs must be somewhere with you from that time, I decided to wait till I get money to buy a better PC to see if anything changes before answering him again (any day now... I hope). Anyway, here are my most recent logs and stuff, hope it helps somehow (I've always had those FPS drops since I know myself as a LoL player, but just recently they have become incredibly difficult to handle during teamfights, specially in Dominion).

Oh my God I'm so happy to see this issue being looked into, League of Legends was half my life and I just got tired of this issue and quit playing a week ago - I can't wait to be able to play again.

Today, every game has the FPS deop...