The difference in weight does not make me want to run aluminum blocks unless they are blown or supercharge, the ring seal on the starting line versus how much the sleeves change in a aluminum block dring the run makes me stay away from them.

A friend of mine saw the crankcase pressure go from 12 inches of vacuum on the starting line on the 1/4 mile tracks go up to1.5 lbs. of crankcase pressure on a mid to low 7 second car with his aluminum race motor compared to his iron block race motor starting the run with 17.5 inches of vacuum on the starting line and cross the 1/4 mile finish line with 12.0 inches of vacuum.
I'm pretty sure they got a lot less runs (25 to 30 more runs on the iron blocks) out of the rings also on the aluminum race motor compared to the iron block race motors