Your post was unclear and I asked what you meant. I didn't debate anything. i was extremely clear and explicit about this. i asked a question, said i didn't know, said i was curious, didn't dispute anything you said.
Only a domain expert could be expected to automatically know whether double GPUs is effectively the same thing as double CPUs or not. Apple has put a lot of effort into making their GPU structure effective (in general, not just for a few special cases), and I didn't know if you were saying they'd failed or not. i know parallel processing is hard, but i also know apple has smart people who've worked on it. i don't know things like whether "lack of unified memory" is a problem for apple's design too, or not. it seems completely plausible to me, not knowing the domain that well, that apple could have had something that works well in general, or not – i don't really know and you didn't say, just assumed your reader would somehow know what you meant (which will basically only work for people who already know your point and have no need to read your comment at all).
His entire point boils down to "GPU Compute (of all forms) is overweighted in comparisons between the Mac Pro and other workstations".
He got antsy because from his perspective, your question definitely seems kinda out of the air. In his original comment, he's basically implying that any GPU based compute solution (so these can be plain gaming optimized GPUs, the "professional" GPUs, or compute optimized GPUs) aren't worth is for the majority of use cases.
The "second card" he talked about was the Xeon Phi, and he makes the differentiation between it and other "GPU based" compute solutions since Xeon Phi consists of a "large" (sub 100) number of relatively simple, but full blown CPU cores (for example, the current Xeon Phi is based on an old Pentium core, the next gen is supposed to be basically an Atom core). This should, in theory, make it easier to exploit parallelism.
Only a domain expert could be expected to automatically know whether double GPUs is effectively the same thing as double CPUs or not. Apple has put a lot of effort into making their GPU structure effective (in general, not just for a few special cases), and I didn't know if you were saying they'd failed or not. i know parallel processing is hard, but i also know apple has smart people who've worked on it. i don't know things like whether "lack of unified memory" is a problem for apple's design too, or not. it seems completely plausible to me, not knowing the domain that well, that apple could have had something that works well in general, or not – i don't really know and you didn't say, just assumed your reader would somehow know what you meant (which will basically only work for people who already know your point and have no need to read your comment at all).