here is my dxdiag, but I insist in this being a major problem of the last update, riot....since the game was running fine before upating for everyone....
Also, it looks like the PvP.net interface is a bit slower since last patch too (but this is minor compared to the in-game fps drop tho)
I understand you tried to improve shadows and some effects but it needs to be optimized before bein implemented....
I hope the report helps you to fix this issue.....

Extra info:
Video: Nvidia Gforce 8600gt (512mb)
Processor: Intel Core 2 duo 2.13ghz (4.26ghz)
Total RAM: 2 Gb (1,7gb available with just windows xp running)?

NOTE: im not using a laptop or a portable device and the temperature is constantly monitored by me (this is not related to a heat issue for me)

So some more information need.

Have you tried disabling the sound in game?

Also can I have some r3dlogs from those games: http://support.leagueoflegends.com/e...f-legends-logs

Note in this thread is specifically about framerate issues not disconnects or lag issues.

In my case, this sometimes deteriorates to a straight freeze of my ability to move/use abilities and frequently even to a DC. Attempting to reconnect causes the PVP.net client to pop up a "Session Closed" message, forcing me to restart the client to reconnect. The client also randomly goes "session closed" at other times as well.

Infos:
Processor: 2.2 GHz Intel Duo Core
RAM: 4 GB
Graphics Card: NVIDIA GeForce G210M

DxDiag: http://pastebin.com/tupLL5e0

Theres my red log

My pc was stable 60 fps always
now it's ranging from 55 to 62 but I can clearly see the game laging (gpu lag) core2duo 4850 4gb no reason to lag....

Can anyone confirm this for me. I'm not sure if i have internet lag or the fps lag because the problem I have is the game sort of freeze for like 2-3 seconds almost every 10 mins during game.

After I disabled all sounds as you said my FPS loss that usually happens on 5 minutes of the game , has just happened after 15 minutes of game
I was happy just before the game reach the mark of 15 minutes lol (OMFG MY FPS ITS NORMAL AGAIN)

Im glad to see that Riot finally is worring about the issue...
I also noticed that some skill auras dont follow the character correctly after the patch (like frostfireannie's molten shield...If I have to describe it, the fire sphere looks like it vibrates on the character while moving (no probs when she is stand still))

Here are my r3dlogs from 2 games pospatch....
In the first game I turned shadows off....and in the other one I used high shadows....

Update: I tried another game today (uploaded the log in this post) and I noticed that the shadows look and work like the old patch in classic summoners rift ,but they look diferent and impact more on my fps in summoners rift autumn for some reason

Note: have not tried the sound thing yet, but the lag, for me, does not occurs after a period of time, it occurs when there are too much effects displayed at the same time, and in Summoners rift autum it even happens whenever I have the shadows on (please remember that I had every setting on high before the patch with 50+ fps)

Attached files:
25/8: Summoners rift autumn 5v5 (changes shadows?)
26/8: Summoners rift 5v5 (same shadows as previous patch)