Long reply here which might shed some light as we've just switched Y11 DS from Triple to Double (AQA Combined)
He's in a school where 3 classes do Double and 1 class does Triple.
He's been a 6 sometimes a 7 since Y9 when they started the content but despite working at full capacity he got three 6s in his mocks which was disappointing as was aiming for 7s. His classmates got 8s & 9s
School have never pushed us to switch but have said it's always an option as he is borderline. He likes Triple because he's in with all his friends.
I asked at the post-mock parents evening just before half term what a switch would entail given he is unable to 'go up a gear' for the looming GCSEs and got a really honest & frank response from each of the 3 teachers. It would be a smooth transition after half term, he'd likely get 2 much stronger grades vs risk three 6s, he could cut down his revision content by a quarter (it's not quite a third) and there would be no impact on A level choices or stigma. DS was sold & decided on the spot to switch.
I spent half term comparing the Triple and Combined Specifications as wanted a list of what Triple content to cut - it was about a quarter but crucially it was all the really quite hard stuff.
Ds is now sitting Combined Physics papers weekly for homework and is getting 9s.
The papers are 1 hour 15 min each rather than 1 hour 45 minutes, there is less content to revise and the harder content & questions are dropped
We are both so relieved to have made the switch at this late stage. The volume of content for GCSEs is just vast and this has slightly taken the pressure off all the other areas he needs to address!
Hopefully he'll get two much stronger grades than risk 3 lower grades.
Do Triple if you are a science natural, find it easy and love it. If you have to work at it go for combined.