anyone moved from B4 to international firms? Yes, but if you want to have a better chance, go for Corp work, it's a lot harder as a liti assoc.

At which PQE (sg scale) did you move? Most move around 2/3 PQE, due to UK's 2 year trainee scheme. You maybe downgraded to UK NQ level at 2 PQE.

what were the salaried before and after the move? I assume you mean what is the difference in salary scale for b4 and int firms. It depends on which "int firm" you go to, whether they are paying cravath scale (rare), MC scale, transatlantic scale, or some other int scale. But you definitely will get a pay bump as a 2PQE SG associate because SG associates are criminally underpaid in general.

what about the hours? More focus on BD, the yearly billable requirement usually stays the same or may even drop. Again, depends on the int firm and the b4 dept you came from, there isn't a one-size-fit-all "all firms are slacker/longer hours than b4".

did you make a move out of a recruiter’s referral? Other than the top-scorers, a lot of people are referred by friends or just self-apply. Cold recruiter calls doesn't really work unless they have a mandate. Remember that the recruiter needs to be paid, so companies are more willing to take you directly than having to pay added costs (barring certain exceptions like a highly specialised field/team that no one wants to go to).