Ring seal is much better with an iron block, hence Pro Stock still using them.
I know you said for street use but my thinking is that the iron blocks will seal up better than aluminum block with steel sleeves will when being driven at normal running coolant temps.

For all the naysayers saying all or most of the new cars come with aluminum blocks look at the new Challengers with the Hi Po motors using iron blocks instead of aluminum.
The new cars blocks were designed for that application, the aftermarket replacement blocks for early American muscle car motors weren't designed to be better than the original iron blocks were.