Depends on what you want and if your lazy.?

Could get away with doing the whole lot with 6mm and no tool changes but would take longer due having to keep shallower depth of cut for 6mm cutter with 30mm plus flute length.?

Or could use 10mm that would allow to hog the whole lot away quickly with deeper DOC and just have larger radius in the corners.

Or if really need tight corners use combination of both 6 & 10mm. Use large cutter to Hog the 98% material away then run round twice with 6mm. One profile pass to fettle corners then another full depth to clean up.

If the radius doesn't matter, which in your case don't think it does then I'd use 8 or 10mm has they will allow more DOC and speed up the Job with no tool changes. . . 8mm would be my preference.!