How good is the original 5D Mark I compared to the 2013 Canon's?

I'm seeing the original 5D Mark 1 body's for sale for very cheap now.

My question is, considering this was a ground breaking full frame camera launched in 2005, have the amateur enthusiast range now caught up with the original 5D (I use the 600D, which is almost identical in IQ to the current 650D) in terms of IQ?

Or does the full frame sensor on the original 5D still offer superior IQ compared to any of the current 'less than $1000' Canon's?

Clearly the new range of Canon's have improved video, but since day one of owning my 600D I have not shot 1 second of video, I use my camera purely for photography. So this aspect of the Canon's doesn't interest me, I'm purely interested in IQ.