If we want to cap the time of downloading overhead the latest block to say 1%, we need to be able to download the MAX_BLOCKSIZE within 6 seconds on average so that we can spend 99% time hashing.

At 1MB, you would need a ~1.7Mbps  connection to keep downloading time to 6s.
At 10MB, 17Mbps
At 100MB, 170Mbps

and you start to see why even 100MB block size would render 90% of the world population unable to participate in mining.
Even at 10MB, it requires investing in a relatively high speed connection.

Also of importance is the fact that local bandwidth and international bandwidths can wary by large amounts. A 1Gbps connection in Singapore(http://www.starhub.com/broadband/plan/maxinfinitysupreme.html) only gives you 100Mbps international bandwidth meaning you only have 100Mbps available for receiving mining blocks.