Answer from cs61c-bb (Jennifer Kelly 16056341) for Question 2
Using the rightmost bits of the address distributes neighboring addresses in neighboring locations in the cache, rather than all in a single block.  With low-bit mapping, the process of finding the correct entry within a cache block involves a comparison (of the upper bits of each entry with the desired upper bits) which will likely terminate before it has reached the end of both numbers, because the block is likely to be sparsely populated.  With high-bit mapping, the same process will often take much longer, as the block will be densely populated due to spatial locality.