A variation in 'straight in feed' is what I would recommend if you must do this with only one tool. This would involve programming in single pass moves, not an automatic routine such as might be used for V threads.
You can pick a Z start point of whatever, say .500" in front of the part. Now create a series of start points that stagger ahead and back of this Z.500 start position. Obviously, at the outermost passes, the tool can be staggered the most, and this amount will have to steadily decrease as the depth of cut increases, until theoretically, the stagger amount is zero with the tool at full depth.
So you can take a cut starting right on Z.5, then the next cut ahead of Z.5, the next cut back of Z.5 and all done at the same X value. Then take the 4th pass starting at Z.5 again, but at increased X depth. And so forth. Keep the chip forming on basically one side of the tool at a time. Keep the rpm up to try to get the best smoothness. Using this method should not get you into overload on your spindle.