I think that since all of those options have an affect on everyone who has shot in the GP series this year it should be opened to all the people in the GP series and not just those booked in for GP6.
For example, if the decision is taken to hold it as the same time as the Masters, then that pushes the presentation ceremony/raffle draw back to a different date that some shooters may not be able to make, clearly that will affect more people than just those booked in for GP6.
I think you could also include - 23rd August, and 25th August (Emley double header) and you could pad out the side effects of each option. For example, moving to a date after 24th August will move the presentation ceremony and raffle draw, and Leaving it out will mean taking the best 4 scores from 6. Unless there are two options - Leave it out (change scores to 4 from 6) or Leave it out (still take best 5 scores from 6).