Lagging while using Zed's ultimate

Hi, whenever I use Zeds ult plus my Q with the 2 shadows I lag so bad that I cant do that. I get 60 fps constant with shadows etc etc, but when theres 2 I lag like hell. Any fixes? or anyone have this problem? I have a decent computer and I dont lag that much unless its a BIG team fight. Thanks :)

There is also reports of people getting the same problems

http://forums.na.leagueoflegends.com/board/showthread.php?t=3934984