I absolutely agree with you that the AMC problems are an excellent set of problems, and very much relevant for the high scorers on the GMAT. I recently wrote about it in this post:improving-q-from-a-50-to-a-145212.html
I actually went through all the AMC questions and curated and assembled only those questions that I believe are relevant for GMAT test takers. Here is the link to all such problems on my site:http://www.gmatquantum.com/amc-questions
I do want to emphasize that many of these problems are not meant to be solved in 2 minutes, actually many can be, after all the test allocates three minutes per problem! But they are tricky and for GMAT purpose I would recommend just struggling with them and forcing your brain to think in as many different ways as possible.
Dabral, thanks for cherry picking the problems and listing down along with the answers. Those looks like a great practice!