the aluminum calipers would still have heat soaking issues that would in turn boil brake fluid, create uneven expansion in the piston housings of the caliper causing slight leakage, etc. All the things that contribute to brake fade, the iron calipers would still be a better heat sink and therefore superior. The amount of weight savings would be negligible versus the overall performance of the caliper. All setups will get some form a brake performance fade of one kind or another. The object is to minimize the extent of performance issues that results from it.
1992 Nissan Skyline GT-R Gunmetal Grey - Long Live the Z and Godzirra! - "Love cars. Love people. Love life." - Mr. K.