I am not following this:

>"A CRC32 over a couple megs of data is only good enough to likely catch "gross"

The CRC on TCP MSS or on the ethernet frame would never be higher than 1460 or 1500 byes(or 9K in the case of jumbo frames), how or where would a CRC over multiple megs come into play in regular networking?

CRC is used on jumbo ethernet of of sized of 9K and it works just fine. In fact this is the reason that 9K is the limit on jumbo frames.