Of course under the northern proposition, the slave states could have increased their representation by freeing as many slaves as they wanted.
Under the southern proposition, the slave states would have no such incentive to free their slaves. The compromise would provide some, but not quite as much incentive to free their slaves.
North Carolina permitted freedmen to vote until 1835, and those freedmen counted as a full person toward representation.
It took Lincoln's invasion of Virginia to finally push them over the edge.
Even in the election of 1860, both states votes for the conciliatory Constitutional Union Party (John Bell).