Hit and miss. I think it really depends on the loading. My birthday flying experience: I got denied once on a long haul J-F, Diamond status then, and got upgraded once on a short haul, Y-J, Gold status then. Plus, you're not actually flying on your birthday. So, not sure what the formula is with status, flying class etc.
I also think there is an old post on this too.
Good luck. Let us know how it turns out.