@seb530 with a drinks package - you need to do approx 8 drinks a day to make the drinks package pay for itself (not a problem for any true Brit lol). However remember it isn't only booze, it covers fresh squeezed juice, posh coffees, waters to take ashore too. Not sure if you are on Wonder (you mentioned the biggest) but if you are then she is truly incredible, mind blowing, has some amazing venues (namely the Mason Jar) where it is great to sit in a rocking chair listening to music and not worry about the cost of drinks. Or sit in Central Park under the stars.
RCI is far superior to P&O in everyway. You will not be disappointed. And if you pay for the drinks package in advance then it is out of the way and you can forget about it! It will be much more expensive to buy the package on board.
Not sure when you are sailing but there usually is a sale around 4/7 weekend. You can buy the package now and if it is cheaper in July you cancel and rebook it at the lower price. Caveat is that it can take a few weeks for the refund to appear.