Look up a glide polar, on that, you can see, that the polar slides on the line which is tangent to the optimum speed point. Therefore, as described above, the speed of max L/D increases (as well as the associated vertical speed, however, the ratio stays the same).
(altough, sometimes the actual glide ratio can vary on gliders with the ballast, especially on the longer ones, as with water on board the wing is more stiff, helping to stay at the optimal shape at high speed, more likely with older designs)
