As for the overall poll, according to page # 26 of the following site, they polled Democrats between 6 and 7 % higher than Republicans:
http://msnbcmedia.msn.com/i/MSNBC/Sections/A_Politics/_Today_Stories_Teases/August_NBC-WSJ_Int_Sched.pdfStrong Democrat ............................................... 24
Not very strong Democrat ................................. 10
Independent/lean Democrat .............................. 11
Strictly Independent .......................................... 13
Independent/lean Republican ............................ 12
Not very strong Republican ............................... 9
Strong Republican ............................................. 18
Other (VOL) ....................................................... 3
Not sure ........................................................... 1
+ Results shown reflect responses among registered voters.