How efficient are our tailplanes?

Hi folks,

In order to get the best performance from the gliders
we fly we need the C of G near the aft limit.

How much difference does this actually make?

Or is it just perception ?

For example, If I add 60kgs of ballast to my Discus,
I should put 2kgs in the fin tank. How much drag penalty
will I incur by not doing so? Do I lose more by adding
tailballast & sacrificing stability than I actually
gain in reduced drag?

(Hope this thread doesn't go on as long as the ballasted
pull-up one :-))

Kevin