I would do the counter-clockwise NE state capitols route :

Providence, Boston, Augusta, Concord, Montpelier, Hartford, PVD.

The slowest part of your trip would be Hartford to Providence, but since you would be heading back to PVD, you can take the faster 'southerly' route on CT-2 most of the way which is up to interstate standards, and avoiding 'Suicide 6'.

Map from Hartford to PVD

Also be advised that the 'Big Dig' tunnels in downtown Boston (parts of I-93 and I-90) are sometimes closed during late night hours for maintenance. The detours are well marked and at that late night hour should only add about 10 minutes to your drive. Since you will be exiting anyway to see the State Capitol it shouldn't make that much of a difference to you.

http://www.masspike.com/travel/construction.html