I believe you would only be up for CGT for the difference in price for the last 6 months. I also think that you can still decide to treat your old PPOR as your current PPOR and not pay any CGT at this point. Naturally this will mean that you will be up for CGT on the increase in value in the first 6 months of your new PPOR when/if you sell this.
Things to consider would be which property has gone up more in the last 6 months and how long do you intend to live in your new PPOR.
Maybe you should discuss all this with your accountant before you do anything else.