Would opt for Westminster - a much nicer school in my opinion and not a hothouse. Unfortunately I cannot offer advice on the admissions although DS sat the 13+ pre-test which they do in Year 6. Maths, English (comprehension, reading a story and writing the final two paragraphs) and VR. All boys are interviewed regardless of results which is not the case for CC. WUS are looking for innate intelligence and a quirky spark.
Depends where you live? Depedning on that the the tube commute could be dire. and bear in mind that the W playing fields are in E London. We were put off after reading John Rae's book - if it was druggy in 70's dread to think of how it is now...
The playing fields are in Vincent Square , Victoria. Westminster Under School is across the road and it's less than 10 minutes walk to the 'Great' School.
CC/St Paul's has a reputation for a large number (not all so not attacking anyone on here)of pushy parents who are only interested in exam results (not a rounded child) and most CC boys that we know seem very unhappy, like coiled springs with poor social skills. There is also a culture of putting boys down who are not as bright (eventhough they managed to get in) and all in all our friends have been quite surprised and feel the environment to be too harsh. I would never send my sons there, even if we were offered a huge scholarship - see G55, I'm not totally biased! I did enquire a very long time ago about DS going a year early and they said to me "No, because it will affect the league tables". Well, frankly, that spoke volumes too me!
But didn't St Pauls pull out of providing data for the league tables. The head there - who seems to be spending a lot of time on press work as Dr Rae did in 1980s -has made a name for attacking the league table culture.