I'm sure a Kings parent will be along shortly, but I know a bit about the school as I know several DC there (I work locally).
I had a look around for DS1 when he was Y5 (we rented so had a certain freedom of secondary school choice which we decided to exercise!). To me it felt very much like my old GS though I am old
. Yes, they are rigorously set; my friends speak of back-seat conversations between DC as they drive a mob to sports fixtures about who's in which set, who's up, who's down. I gather they have a system where you get 'set' for a block of related subjects rather than for every subject? Like if you're good at maths, you're also in a high set for MFL...
I have been told of there being a bit of a divide, socially, at the school between the DC from the posh MC villages that surround Winchester and the DC from the large council estate, Stanmore, in Winch. This person (who's DC had been a head child at the school recently) said the twain didn't tend to meet. Also, the school in this DC's opinion, appeared to only laud its Alpha acheivers
I hasten to add I'm only telling you what I was told. I can't corroborate any of it!
For the record we didn't choose the school as I was concerned that, though DS1 would probably be in set 1 (not A, maybe C) for most things, DS2 wouldn't as he is less academic (thus risked being in lower sets with not only the less able but also the disengaged and disruptive, not that Kings necessarily 'suffers' from this!) so we chose a nearby comp that effectively doesn't set yet, in fact gets better GCSE results fwiw than Kings; our choice is vair MC, however!
So might not suit every one.
On balance, I believe Kings is a good school with a good reputation. You just need to decide if you want a GS feel or a Comp feel to your DC's education (assuming your DC will be in the upper end of the setting continuum at Kings, not labelled as a 'fail', or that you're or they're not too worried about how public declared averse setting might affect them).