Just wanted to share my experience with Oundle. Certainly not negating anyone's bad experience with the school's pastoral care and I hope those children are happy now.
I left Oundle 6 years ago and have met people since from all the schools listed above. Oundle wasn't for me a pastoral inferno and neither are the others, particularly Rugby gets good press, the pastoral utopias. I know some at all who didn't love their time, don't think Oundle is, in general, any worse. But clearly some have had bad experiences so hoping they found the right school. Oundle, Uppingham and Rugby have same set-up, all eat in houses which I really loved. All have day students but are run as boarding schools so day students have to fit into this rhythm. Day students at Oundle in separate house didn't affect their integration at all, we all hung out together on weekends and after school too etc. All are in a town: Oundle is beautiful. Rugby isn't very nice but not sure it affects the students too much. Uppingham quite a nice town too. All can interact with the town which helps to not be bored.
Oundle is an excellent school, and would be my preference over Rugby or Uppingham. Out of these it has the strongest work ethic, and students' approach to anything is always serious and they try their best. It is the school's USP and parents choose it for this reason. They also do give you responsibility more than the others e.g you take charge of your house plays with no adult involvement. Students take this on with them when they leave too. Oundelian's work ethic comes from the students. It has the widest pupil profile/interests of the three in my opinion and the large size is a benefit. You don't have a social group that dominates a year as much, everyone finds someone who is similar to them and probably shares their interest (even the slightly whacky ones).
Grades wise, you can't compare them. They all do different exam boards. For an academic child Oundle has best provision. Uppingham and rugby don't do nearly as many pre-u (MUCH HARDER AND TAXING a level equivalent) as Oundle and also unless there is same subject percentage spread then it isn't a fair comparison. I know Uppingham you can do business studies at Oundle you cant. Couple this with more Oundle students going to america and sitting SATs (so, only guessing, not needing to take a levels seriously but this is just a guess), then it is hard to make comparisons. The PRE-U ends next year and Oundle and other more academic places like winchester back in the a level mix it will change the a* spread among schools. Oundle have dipped slightly recently which I have found strange. Maybe good to put the admissions department on the spot and ask them why haha.
Other ones mentioned:
Marlborough - fantastic school, really like the people from it and most similar to Oundle I feel, tiny bit less academic. Bit flashy/snobby apparently but most mellow when leave.
Wellington great too (lots go home at weekends) good grades but not sure its from a natural work ethic from the kids.
CH great school and super grounded and always liked people from there, can get on with anyone. Also they seem to pursue own interests. Not as academic as others above but its good
Teddies - Pretty average (weekly boarding there now but if lots stay at school shouldn't affect full boarders too much). Im sure kids thrive there but, ime, people seem a bit boring and samey.
Also, just a heads up, if a school is amazing, doesn't mean your child will thrive and even do better than in one that's less academic etc. Successful people come from lots of different types of school. Most important should be a child's happiness in a place and they normally know within an hour or two when they walk around if they like the vibe and the people. Hope the above helpful - GOOD LUCK WITH YOUR DECISION!