There's a thread for stuff like this. Use it:
http://facepunch.com/showthread.php?t=1334691
Oh, and you probably shouldn't read any of the stuff i wrote below. I just write stupid sh*t like that because it pisses me off that people actually waste their money bying a mac. Anyways, don't read it. It's just gonna offend a bunch of people... I should probably just delete it, shouldn't i? Yeah, i should. I'm not gonna do that though.
1. Mac... Thats half the problem right there. Oh, and it proves that you are going to burn in hell. I don't really believe in a thing such as "hell" so i wouldn't take that as much of an insult though.
2. iMac... Proof that intelligence is a part of you. Its basically any other mac (Exact same software and hardware), its just not portable.
3. The main problem here is probably your specs. What GPU and how much RAM have ya got? And what 'bout your CPU clock speed and version? You telling us that its an i7 says pretty much nothing about your computer.
Edit:
I just realized that the link i posted may not be for these kinds of problems, but i still think that you should take a look for a solution there.