Advice needed on Prep Schools, St Swithuns compared to Forres Sandle Manir

[Mumato1]

Can anyone give me their experience of either of these schools or recommend any others? DD is very able, currently at in pre prep (starting yr 2 in Sept) but looking to change schools as her current one is very focussed on the less able, something we weren't aware of when she started there! She's not really being stretched. Would love to know opinions of parents with children at prep schools Hants/Dorset/Wilts area. Thank you 😊