I've been shooting with a lead sled for 5yrs or more now, started with the original and have the DFT now.
What is even more important than the amount of weight is the surface your shooting on, if your shooting on carpet or some surface that does NOT allow the sled to slide back into your shoulder then don't use any weight at all, you shouldn't really shoot on carpet at all, wood is not as bad but it still grabs and doesn't slide well. The best thing to use is a composite table like the Caldwell stable table, I have one and it works perfect. I use either no weight or 1 25lb bag of shot with this setup, either way the sled will slide back into my shoulder with turkey loads, that's very important in order to safeguard against damage to gun or scope.