The myths about write speed department.
These are your available speeds with the current combination of media/firmware/burner: Speeds: 3x, 4x, 6x
You set it to 2.4x in both versions. You get 3x in both versions. The only difference is that the later version informs you about it.
Conclusion: 2.4x is an impossible speed - as you got 3x in both versions.
If I had a burner with that many issues, I would give it a one way ticket to the nearest dumpster and get a good external USB burner. Just the amount of the current coaster rate should soon have paid for such a new burner.