Filling speaker stands: sand, lead, steel, rice. Full, half, etc?

With my proac tablettes, I am using 28 inch speaker stands which have two round steel tubes about two inches in diameter.  The stands have spikes into my wooden floor (through carpet) and rubber pads on top.  I have a rather small room 12x12, and I have played around with the speaker positions in the room, finding a pretty sweet spot optimizing the bass and soundstage.  I have done all this with the stands unfilled.

so I am looking for advice on filling the stands. What do I use: sand, steel shot, lead shot, rice?  Do I fill them half full, three quarters, or full? Do I fill all the tubes the same? Can overfill makes things worse?

like most things (i.e. speaker placement) I suspect there will be some trial and error, but as it will be a real pain in the rear to fill/empty/refill the various materials to really compare, I am hoping that there are some lessons learned that the rest of you can share with me to get me pretty close with my first trial.

Alos, what effect will the filling have- should I expect deeper bass, bigger soundstage, greater depth, more detail, or..... better yet what should I not expect to change? This will help me know what I should be listening for as I tweak things.

and finally, should I expect my current optimum speaker position to change with filled stands? Will I have to go through the whole positioning exercise again?

thanks, ( and happy new year)

Back when I had Dyn C1's I used very dry sand to fill them about 2/3 full. To me the sound was more coherent. Not sure I remember how the sound changed but I did not like the way they sounded when full. Also since the Dyn Stand4 had 2 posts one front and one rear I had a tendency to put a little more in the rear posts to balance it out. The Dyn C1's are front heavy since the driver is in the front and sticks out a bit farther.

As far as how full to fill them I would just try a few combinations and see what sounds best for you.

Good Luick 
i think sand is the best filler.  its small and absorbs a lot of energy.  The height is dependent on the height of the speaker stands.  you dont want to make them top heavy but the more sand you put in the better they dampen any vibrations.  Filling the stands with sand, or lead on the bottom and sand filling in the gaps then sand higher is similar to making the cabinets less resonant.  Helps the speakers bring out details and tightens their low end by avoiding vibrations interacting with the drivers intended movement. 
I use playground sand (sold at my home depot) mixed with lead shot and apply evenly distributed but do fill to the top. I have used this on speaker stands in the past and still use on my Lead Balloon turntable stand where it tightens everything up, I have found that the added mass was always a positive.
No idea on how much or what you use would affect sound, but be aware that lead, if ingested, can have an adverse effect on cognitive development. If you have young children in the house and decide to use lead shot, you should fill and adjust in an area that the kids will not have access to.  Pouring lead shot will generate lead dust, and children will invariably get dust on their hands and clothes and from there, hard to prevent it from getting into their mouths.  In the future, disposing of the lead could be a problem, also.  Just my $0.02.  You may evaluate the risk differently.