GTY rates are standard rates that come out once a category starts to fill up. And because of this, that rate tends to be higher than opening day rates. It is very possible than a category goes up in price, while another category doesn't move.
Also, any upgrades you request from DCL before or after PIF, would result in rates based on your original booking day. This could lead to a lower price for a higher category, or a very small difference.
Hope this helps...
Hmmmm not following all I know is it cost me a smidge to move from a 5E GTY to a guranteed 4E.
Are you saying the day I booked the 5E GTY it was only a "smidge" to move up to a 4E so I should have done this originally?