"Centralization of mining due to slow propagation with bigger blocks" is mostly a strawman argument.
Even if the blocksize went up to 8MB with no increases in Internet speed,
you're talking about 8 seconds difference between an 8mbit connection and
a 16mbit connection. Compare to the 600 seconds required to solve a block
and you get 8/600 = .0133~. So that's a 1.3% advantage to the faster
miner. Quite dubious to say that would be a crushing competitive advantage
given that there are other factors involved in mining costs such as electricity,
gear, and operations.
Sry, I can't follow your numbers there with regards to block propagation. But mining centralization has already largely happened because of the economics of Bitcoin mining.
Mining centralization already happened but small blockers are afraid that the geographic area or region with fastest internet speeds will become the only
place mining will be competitive if blocks get big. But I'm not buying their argument.
As far as the numbers, there's 8 bits in one byte. Therefore, a difference of 8 megabits in speed is one megabyte per second.
If block size is 8 MB, that's 8 seconds. Yet it takes 10 minutes to solve a block so 8/600.