Gold Nugget on the Volk will beat the cocktail on C-35 in terms of size. As to the quality, that is another issue.
If you don't prune the tree, the cocktail would be larger than gold nugget on C-35. Grafting on the same rootstock, cocktail always grows higher. As to how high ultimately, I haven't the luxury of time to find that out myself. The gold nugget is relatively new. Who has a ten year old Gold Nugget tree for example aside from UCR?