I can say with absolute certainty that an iron BBM block is the strongest FE block that has been produced to date. Not knocking anyone else's effort, that is just a fact. I have had over 100 BBM blocks pass through here. Two blocks have had MINOR issues that were easily corrected. One block had a major issue, and BBM replaced the block, no hassle. Really good percentage of success in my opinion, and the man rectified the situation on the one with a major issue.
I can say with absolute certainty that the Shelby designed aluminum block was engineered and intended to be produced only as an aluminum block. It is the best aluminum block, hands down, but you are going to pay for it.
I can say with absolute certainty that with the same exact engine at the 900-ish hp level, there is 30 hp difference between an iron BBM block and a Shelby aluminum block with neither having a vacuum pump. The iron block being superior. I think a Shelby with a vacuum pump is just about even with an iron BBM with only pan-evacs. A vacuum pump makes any of them better. It makes more difference on an aluminum block.
I have repaired several Pond aluminum blocks with high horsepower and compression that have experienced main bearing issues. They need a step above the threads at the parting line, and they need a deeper rooted main stud. It cannot be made as strong as the Shelby as it is currently being cast. I will say however, that the cylinders and head fastener design in the Pond blocks are at least as good as the Shelby. I have seen the Pond cylinders come back after thousands of miles and hard running, and the cylinders are pretty good, and they hone very well.....may stay at home a little better than a Shelby, but the main web situation is notable. The mains have to survive for the engine to survive......
The BBM aluminum block has better main web structure than the Pond. The ones I have seen could benefit from using longer studs. I think that is probably going to happen at some point.
I believe that an early centeroiler might be a touch better on ring seal than an aluminum Shelby, but I think the Shelby mains are stronger than OE iron.
I think an OE side oiler is tit for tat with a Shelby aluminum in terms of ring seal, but as with the centeroiler, the bottom end will not stand the power that a Shelby will.
All of the above is based on what I have seen and what I have used. Just my observations and opinions......