Aluminum exhaust manifolds an upgrade form cast iron manifolds?

How do aluminum exhaust manifolds compare to cast iron for longevity and reliability? I'd like the weight savings (on a small block V8) of the aluminum over cast iron. But does aluminum hold up with modern coating, or does the heat factor make exhaust manifolds a part that cast iron is better despite the weight?

Looking at HGE or Barr or GLM aluminum manifolds based on price, although I see there are some much more pricey options out there which may be coated better for longevity?

 

I wouldn't trade the lighterweight of aluminum for the increased dissimilar metal corrosion one would suffer running raw water through the manifolds, even a freshwater cooled with raw water dump would be something I'd stay away from. Freshwater guys don't seem to have near the problems, aluminum heads and manifolds too. Somebody else will undoubtedly chime in. I'm interested in the concencus, but wary.

 

A better choice would be nickel alloys 825 (Incoloy) or 625 (Inconel).