(I have an A850, but lets assume it behaves similarly to an A900 for now).
I read the monster thread on the optimal ISO (200 vs 320) for the A900. If I understand correctly, ISO 320 is the lowest ISO that doesn't clip blacks. You give up a bit of dynamic range and slightly increase noise with 320, but some people view it as a worthy tradeoff to avoid clipping.
My question is this: how can I tell if am actually clipping blacks? In Lightroom and Raw Developer I usually start by adjusting black level and exposure to a point where I see no obvious clipping in either blacks or highlights, then make further adjustments to the image. I'm new to the A850, but I've shot a bunch of images at both ISO 320 and ISO 200 and I haven't ran into a case at either ISO where I felt like blacks were severely clipped (except for totally underexposed images).
Am I missing something? Are my raw converters lying to me about black levels and there is clipping happening that I don't see? Really curious to hear everyone's thoughts -- I want make sure I'm not missing something obvious.