It's a tricky one, I'd say that if you're used to shooting in the FT sitting position, then you'll gain some advantages shooting SFT.
First off, not all recoiling guns like being rested against a peg with the butt on the ground so you might be able to get a more consistent position shooting from the sitting position.
Bracketing is likely to work quite well at Anston - we use Nockover targets exclusively with very few custom faceplates. However, bracketing from the FT sitting position is more difficult than bracketing from HFT prone.
Another advantage of SFT for the Championships is that you can have a windicator and spirit level fitted if you like (although personally I don't find a windicator helps that much in the Anston woods).
In SFT you can also adjust your parallax for each lane (before looking through your scope) so you'll gain an advantage on parallax error for the longer shots.
Whichever you decide to go for, I'm sure you'll really enjoy the day