Have owned both, nothing wrong with running a aluminum blocks on the street, yes some of the old KB water block, due to there design, and sleeve construction would typically find water in the ol etc.
Those days are over with.
It really a matter of preference. Yes, for a fact the aluminum block gives up some power over the same iron brother. Some top engine builders say this approaches 50+hp. Some say 25-30hp. Its easy to understand just by looking at the lash growth between iron vs aluminum. Aluminum blocks lash grows near 100% more than iron. For example, my last iron block aluminum head engine, lash would grow .005-.007 from cold to hot. Keeping everything else the same, same heads, same rocker arms, even the same pushrods, the Indy maxx block grew .012-.014 inch. I would say this would effect ring seal etc.
IMO
Power loss almost offsets, weight gain. The repearability of aluminum makes it a nice choice. If your building a dragster or a 2200 lbs tube chassis car, then the weight diff shouldn't be much as a factor.
Stripping weight off our old Mopars really isnt a problem, just takes a phone call, and for one to open his wallet.
This debate will never end, and we all have diff idea's what works, and which is better and why.
Its really a matter of preference.
But on a side note, you dont hear about to many aftermarket block failures today. Even with the added community of forums like Moparts. These aftermarket blocks are made to handle about anything the average Joe can throw at it.
In other words, which every block you have, even a nice a nice repairable KB block, a catastrophic engine failure suxs big time regardless of block type.