Cosign what delta and pete say. The bus from london to Papplewick seems fine, loads of boys take it and don't seem unusually exhausted or resentful of the drive - many of them do flexi board here and there as well.
Running through your list, you've got a clutch of good schools there but if it's Eton or Winchester you're hoping for, Papplewick and Summerfields have a higher % of their leavers going to those schools. Papplewick sent 25% of its leavers to Eton in the last 5 years, 20% to Harrow and 12% to Winchester and every year they get academic and music scholarships to one or more of these. And Papplewick is non-selective at the start and is also the smallest of the schools you mention - they have about 200 boys, and from the list of their leaving destinations I think you can see that they're definitely not just focusing on high achievers to the detriment of the rest. (Aldro is only a little bigger at 225, Summerfields and Caldicott are 300 and Lambrook is 560, though it's 3-13 not 7-13.)
That doesn't mean the other schools don't send their boys to Eton, or are less academic, it's just that there is definitely a different emphasis - eg. I know two lovely and super bright boys at Eton from Aldro, but in the last 5 years 30% of Aldro leavers went to Charterhouse, and 12% each to Craleigh, Wellington and Tonbridge, compared to 5% to Eton and 4% to Wincoll - this isn't negligible as this still means 12 to Eton and 9 to Winchester but you can see they are naturally going to prepare with other schools in mind. Caldicott similarly sent 15% of their boys to Eton in the last 5 years, again, this means 36 of their boys were successful so they know what they're about.
So - will Papplewick do the same job as Summerfields, well I think you can see from their results that they both know what they're doing (as do Lambrook, Aldro, Caldicott etc). Boarding is definitely something you have to be comfortable with for your own son - for my own son, I know he wouldn't have coped weekly boarding so early and prefer the Papplewick "build them up" approach, no boarding required initially, build up to it over the years with fun sleepovers and a night of boarding here and there so by the time they're in the summer of Y6 they're practically begging to board.
However...it's better to go with your gut in terms of a school that you feel you'll get on with. Papplewick is unquestionably more eccentric, less sporty and swish than Lambrook. Lambrook is undoubtedly stunning, they do prepare and send boys to Eton, their drama and music facilities were amazing and if you have a super sportsman then they will value that highly. I know one mum with two boys at Caldicott, she loves it and it's right for them.
(I don't know anything about KCW so can't help with that one, sorry!)