League of Legends Framerate strangeness

Greetings,

I have an interesting problem. I have 2 nearly identical aging gaming rigs. My fiance and I have been playing league of legends and she was getting terrible frame rates so i bought a nvidia 560ti for her and she gets around 50 fps but bogs down to <10fps in big fights. On identical settings my 9800GTS will get a solid 60FPS and only get down to the upper 30's and lower 40's in big fights.

what is the source of those low frame rates and what can i do to fix that.

Below are the builds for 2 of my gaming rigs. I know my cpu is a bottleneck i would like to avoid a CPU upgrade is possible but am willing if necessary. What Proc would be recommended for such an upgrade in bilbo?

https://docs.google.com/spreadsheet [...] utput=html

Thank you very much for your time and it is most appreciated.

Those specs where for your comp and not you fiance's, right? A 560ti can play pretty much anything on max settings, so thats not your problem. If you could give the specs of the computer, we could make some suggestions. But, I think it is probably a cpu thing, because big fights are really cpu intense.