Below are the total votes for governor and Senate races for MA in off year elections. The difference is minimal with the 2010 Senate election having the most votes cast.
2002 Massachusetts gubernatorial election 2,220,301 million total votes
http://en.wikipedia.org/wiki/Massachusetts_gubernatorial_election,_20022002 United States Senate election in Massachusetts 2,006,758 million total votes
http://en.wikipedia.org/wiki/United_States_Senate_election_in_Massachusetts,_20022006 Massachusetts gubernatorial election 2,243,835 million total votes
http://en.wikipedia.org/wiki/Massachusetts_gubernatorial_election,_20062006 United States Senate election in Massachusetts 2,165,490 million total votes
http://en.wikipedia.org/wiki/United_States_Senate_election_in_Massachusetts,_20062010 United States Senate special election in Massachusetts 2,249,026 million total votes
http://en.wikipedia.org/wiki/United_States_Senate_special_election_in_Massachusetts,_2010