The thing is, I don't think 2018 will be as large a wave as 2010. Substantially bigger then 2014, and slightly bigger then 2006.
The thing is Republicans were starting from fewer seats in 2010, so a 63-seat gain was more gettable then than it is now. However, while unlikely, Democrats could get around 242 seats or slightly more if the polls turn out to be underrating them rather than the GOP and the wave breaks late for them.
Also, Republicans had a lot more low hanging fruit than Dems do this cycle.
