I am using 25 lbs as recommended by VSA.
Tom, I have no doubt the Sistrums would sound spectacular under most speakers, but lead has it's advantages. It does give some inprovement with the VR2s at far less cost than the Sistrums, and the speakers are much more stable which may be important with kids or dogs, etc. It cost me under $40 to make a big improvement using lead shot. Try it, and if you don't like it, you can easily remove the lead with very little money or effort lost.