Not really. iMacs use the mobile core 2 processors, or at least they did. Also the graphics card options are very limited. And you cant upgrade an iMac. You can put windows on them sure, but they lack a lot of the things pc owners have come accustomed to.
whats this about os not being a factor... yes, it is definitely a factor...
lets take a look at geforce drivers for mac.. how optimized do you think they are for gaming??! nvidia probably doesnt even give a crap about mac geforce drivers!!!
windows is a must for gaming.. end of discussion!!!
how many games do you see in this world that say it is mac supported