I wouldn't get to carried away with reduced loads to much as it can cause a Ka-Boom the same as to much can. Plus the likely hood of squib is increased a bunch. Reducing by 60% seems like you are walking on thin ice. :|
I've never tried loads like you described. And I would be quite hesitant to load such light loads. I have loaded light charges of fast burning powder in lead bullet .45/70 cartridges, but these were documented loads taken from reloading manuals. The charges were SO light that the powder only filled a very small portion of the case. I slipped a small wad of tissue paper down on top of each charge of powder so as to help keep the powder against the primer when firing. The tissue paper burns upon firing and I had very good luck with these loads.
I would caution against experimenting with any loads not documented in a recognized loading manual. As stated above, ultra-light loads can be just as dangerous as over maximum loads due to detonation.
I pretty much stick with the ranges of powder listed in the various manuals. Lyman is the one I use a lot and I have many others. I find the accuracy and target loads specified for most of the powders and bullet weights are very accurate.