At 7+ and 8+ schools are looking for potential as much as achievement. WUS has always taken quite a good proportion from state schools, and similarly will be open to taking some from the French system.
Bilingualism is not unusual in London schools, so probably wont carry a lot of weight, but is obviously a really useful life skill.
These exams are really competitive and not that many boys are ready at this stage. DS would never have been a contender, though had no problems gaining a place at Westminster at 13+. Performance at 6 (which is what 7+ is) is not a great predictor of performance at, say, 18. It is easy to be swept up in the London pathway, pushy pre-prep, WUS/Colet, Westminster/SPS/Eton, Oxbridge/Ivy League, but this will only suit a small minority. A large number of London's private schools feature in the top 100 in various league tables. All are capable of enabling bright children achieve their potential. Westminster is fabulous for the right child, the child who loves education and enjoys being surrounded by peers who feel the same. But equally there can be a real freedom in being at a school where not everyone gets A*s in everything and where you can discover what you are good at and be supported in subjects you find more difficult.
Our observation has been that children transfer from the Lycée at a range of ages. Westminster regularly takes some at sixth form, and at other entry points before then, including 10+ and 11+. The tricky one is 13+, as it is hard work covering the Common Entrance syllabus at home, though it can. and has been, done. However lots of London days schools don't use CE and will be willing to take the right child at this stage. Plus the Lycée is also a very good school, with pupils regularly leaving for top British and American Universities as well as returning to France.