Not the original poster, but any kind of overtime is rare for salaried work? At least in the US.

I'd take 60% per hour for overtime in a heartbeat as long as it was optional, since I've always ended up doing that kind of work for client/manager goodwill (or the pleasure of not being fired).

60% of what was billed to the client; so probably the equivalent of 3x or 4x their normal salary rate.

I understand that you get 60% of what's billed to your client, which probably is several times your salary rate per hour, and not 60% of your regular rate per hour. Maybe?