The Perse is most definitely not competitive. At least not once you are in - all the kids there know that just by getting in they are bright, so there really isn't much competition between them. The school is also excellent at celebrating all successes - sport, drama, music, general knowledge and debating competitions etc as well as academic, so everyone feels that they are good at something. The head makes a point of wanting to educate the whole child - the academic excellence is sort of a given, given their intake. Drama may not be offered as a GCSE subject, but the level of performance is very high.
Pastoral care is excellent - 1 tutor to max 12 pupils, and they have the same one for y7&8, and then one for Y9-11, so they get to know them well. There has been a big expansion, and that has caused some issues - lots of new teachers, many NQT. Some not as good as they may have seemed at interview, but they tend not to stay long. We have had issues with some teachers - but that happens at all schools and what is impressive is the way the Perse deals with the issues when raised. Can't give specifics as don't want to out myself, but everything I've raised has been resolved.
It is big - but it's not impersonal - it just means that there are larger friendship groups for your kids to choose from IMO. The money raised from extra fees has gone to build some impressive facilities - new block and new new block.
If your child is adventurous, POP is a huge selling point - like scouts only much much better- there's exploration, climbing, Adventure racing, wilderness, shooting and canoeing clubs, all run by the outdoor pursuits leaders, which give amazing opportunities to the kids. Really develops their leadership skills as well.
They do do DT at GCSE, but the systems and controls syllabus - so basically engineering. They also offer Computer Science GCSE now - proper programming rather than ICT.
I did like the Leys, but for us one of the main drawbacks was the fact it is a boarding school with some day pupils. And in the later years even they do day boarding and saturday school, whereas at the Perse kids usually leave at 4 (apart from outdoor pursuits clubs are usually at extended lunchtime) I think that's one of the big differences which should inform your choice - and let's face it, neither school is crap, and your DS is going to have a fab education and great opportunities at either.