Mominatrix, this is a reassuring post of yours, especially for those making this difficult choice (but what a great dilemma!). We chose LU last year over the other neighbouring schools, even though on paper (leagues), it's perceived to be lower down, especially for those measuring the leavers destinations success rate to Oxbridge. The list is diverse including the growth in US/overseas, if that's where the aspirations of students are.
I am not in a position to comment on the higher years, and have therefore avoided provided reassurance to those seeking it on this, but I will concur with Abracadabra10 that the teaching is maximised in lesson time, with any spill over as homework only, and holidays as relax, enjoy and read. For the early years.
We chose it because we felt the learning style would be more innovative and interesting. When I ask my daughter now, half a year in, if there's one thing she could change about LU, what would it be, her response is...longer days to fit more lessons in. Not because she's super bright (because she's not, but just LOVES the lessons!). This is on top of her massive extra curricular schedule. I tell her not to share that one amongst friends, as it is most certainly not cool. She is obviously not one of those ones...there really are all sorts at LU amongst the large year groups!
Good luck with choosing Shirleycantbe, you won't go wrong with either.