The difference is small, depends on how many towns get the same ranks and the corruption we might spare here will add to other towns that move back in the list.
The list of towns is ordered by distance and (in C3C) foundation date.
It would be no* difference if all further towns are settled at RCP5,
The Treasury 
would then stay Rank 2 after
The Admirality.
* There will be a small increase in distance corruption (1-2%?) by distance being 5 instead of 4.
Any town we found later at RCP4 will push
The Treasury back in the list and increase its corruption - in favour of the new town. If these are two new towns, the increase of rank corruption might be like 5-10%
All numbers guessed from experience
Someone like to do the exact maths?
The advantage by getting the extra commerce every turn while working food rich tiles is outweighing the corruption disadvantage by far Imo, especially in the short run (growing to 6) but also in mid terms.
Only in long range when we work the hill every turn @size 12, the original dot might be stronger.