This really is firm dependent. At a place like Latham, non-equity partners can make $1.5M+. At a lot of other firms, most non-equity partners hover between $500K-$1M. Some firms it's over $1M, but not as many as you'd think.
If you're originating over $3M, it's worth it to look elsewhere if you're not getting promoted to equity at your own firm. Find a good legal recruiter to talk to (there are a few great ones in DC and many awful ones, do research before working with one of them).