No idea really, I'm afraid, but I'd have thought it was more helpful to try some different question types than the exact level of difficulty. Reasoning tests are meant to be a lot about natural ability anyway. Back when we were doing VR and non-VR practice for 11+, I never found that either DC's scores improved all that much with practice, which kind of backs that up - I mean, they did a little bit to start with, but they plateaued pretty quickly.
It's definitely true that quite a few people take grammar places instead - I remember the school being very open about that on the exam day, and I've met quite a few who got in from wait list.
What a pita about the train strikes, I imagine that's stressful. Doubt they'll postpone though, sorry - term starts before the train strikes finish, and I can't imagine it would be easy to run entrance exams for hundreds of kids on a normal school day.
I hope you manage to get there OK and your DC isn't too stressed about it. It was a while ago now, but I remember being really anxious about how DC1 would manage, as she's not very confident, but actually it was honestly fine, even though she found one of the papers quite hard. She was definitely knackered by the end of the day, but quite cheerful. It was the last entrance exam we did, so it was a nice feeling to finish!