This gov.uk site lists every school; I've taken the liberty of narrowing it down to "W2 plus 5 miles" based on "W2" being roughly in between the two schools you've listed, "5 miles" being doable by London transport. It has various filters you can re-apply to suit.
As to how good they are, one trend I hear of increasingly is that popular state schools are raising their sixth form entry grades from the typical B to A.
For example, St Marylebone appears to have slightly higher thresholds for some subjects than say Grey Coat Hospital, arguably a similar school... likewise Camden sets thresholds in excess of super selectives and independents in some subjects, but has arguably no more value-added than the very similar LaSWAP schools who have a wider range of entry criteria, and therefore lower outcomes...
Newer schools with less track record may also be tempted to raise the entry bar to increase the likelihood of higher results.
Co-ed state sixth forms in central London also offer a respite from fees, especially for boys, so the more "popular" ones may be tempted to set higher entry thresholds.
Raising the entry bar will certainly reduce the value-added needed to achieve slightly higher outcomes than lower entry schools. I always judge that if an entry grade is A at GCSE, anything less than A* at A level means the school is doing less well for its students than a B entry school that delivers B+ at A level. Most of the more effective fee-paying senior schools would have to work with that expectation.
Ultimately, there is no replacement for judging a place on a real life visit. What matters to one may not to another, and you only get one good guess with DC's two years. That may not be the same school that's ideal for someone else's DC.