Had to test this as I saw my name! Simple test with ƒ4.0/50.01 and ƒ5.6/25.00 - exposure looked identical(using some 10-12bit build), so its probably a lens issue @omashow.
@a1ex I added those lines to consts.h in 5D2 folder(from this point on I have no idea if I did it right) and compiled it in the iso research branch, in adtg_gui the first two registers were ADTG1[105f]N and ADTG1, one had the green caption 'Shutter blanking for x5/x10 zoom', other had no text. Canon menu was 23.976fps but for some reason I couldn't get 1/25.00, only 24.99, and no 50.01, only 1/49.95. At 1/49.95 ADTG1 was 0x249, and at 1/24 the register was 0x64. In zoom, shutter 1/29.74, register said 0x3, and with shutter 1/58.06 the register said 0x272. I'm sure that was all wrong but oh well.
So did '0x404b4110/14' mean FRAME_SHUTTER_BLANKING_ZOOM should be 0x404b4110 and FRAME_SHUTTER_BLANKING_NOZOOM should be 0x404b4114?