I have that exact same TV (but no cabinet yet).
I bought some graph paper and sketched out a few different versions of cabinets to scale, with different angles (10 degrees, 20 degrees, 30 degrees, etc). I also measured the TV and drew that to scale on the graph paper. Then, you can easily hold both sheets of paper up to the light and see how it fits at different angles. Pretty cool, if you don't have software.
Like someone said earlier, it depends on the angle mostly. It also depends on how deep the screen is in your cabinet. Generally though, I'm finding 36" to be adequate for most scenarios.