I got the highest i5 available, 3.8GHz. For what it's worth, I had an i5 on my PC, then bumped it up to the next gen i7 (not same gen i7) and I felt the speed difference wasn't huge. Maybe 10% or so faster rendering in Premiere Pro. Outside of rendering, I didn't feel there was a significant difference. That's just my experience anyway.
I haven't done any rendering on my i5 iMac, but I have done some 1440p gaming and haven't heard a fan yet.
I did consider the i7, but figured I'd rather have a quieter iMac than a slight rendering boost.
That's interesting, thanks.