Correlation between IQ and effectiveness does break down at higher IQs, you're right. Nonetheless, there doesn't appear to be any sharp limit to effectiveness itself. This suggests to me that it is IQ that is breaking down, rather than us reaching some point of diminishing returns.

As for uploading, yes, I think it would be great if we could hitch human thought to Moore's Law, and I don't see any reason why this shouldn't eventually be possible.

My point here was that human mind are lop-sided, to use your terminology. They are sorely lacking in certain hardware optimizations that could render them thousands or millions of times faster (this is contentious, but I think reasonable). Exposing human minds to Moore's Law doesn't just give them the continued benefit of exponential growth, it gives them a huge one-off explosion in capability.

For all intents and purposes, an uploaded IQ 150 person accelerated a million times might as well be a FOOM in terms of capability. Likewise an artificially constructed AI with similar abilities.

(Edit: To be clear, I'm skeptical of true recursive FOOMs as well. However, I don't think something that powerful is needed in practice for a hard take off to occur, and think arguments for FAI carry through just as well even if self modifying AIs hit a ceiling after the first or second round of self modification.)