I have no views on the schools you mentioned, but DD is in Y12 and changed for 6th form.
In her case it has been the best thing. The reasons for the change were that she went to the secondary school from a feeder primary, so many pupils were ones she knew from primary and had not always had good experiences with. The boards for the A levels she wanted to take were different from her original school and the matter they covered is much more what she wanted to concentrate on.
DD is now a changed child. The move has been nothing but positive for her. We went to look at a few schools, and she knew as soon as she viewed this present school that it was the one for her.
She was a bit unconfident and worried that people wouldn't talk to her at the new school, but obviously that hasn't happened. She has make some lovely friends.
It has been hard work for her, I won't deny. She's been very tired as she's had not only to do AS level work, but also get to know all new teachers and a new school layout. A few of the school rules are a bit different, too. She had a chat yesterday with the head of Y12 (she thought this was especially for those who changed schools) who asked how she thought she was getting on. I liked that.
She did have to get As/Bs in her A level subjects and also in Maths and English in order to move.
Many of her friends also thought they would move, but when it got down to it, they decided to stay at their old school. I was very surprised. Some pupils have already left Y12 at DD's new school, only two weeks in!
Good luck for your DD, whatever she decides. DS1 didn't change and he was very happy, staying at the same school (which is also the one DD was at). It's very definitely the fact that different schools suit different DC.