Memory speed support is dependent on your Mobo, but iirc, all FM2+ motherboards support at least up to 2133mhz. There have been lots of instances of OCing with 2400 ram causing instability, but usually dropping it to 2133 with XMP/proper stock settings, or even a bit relaxed, have alleviated those issues.
The heat issue may have been fixed by the BIOS reset. If there was a funky setting on the Fan speed in BIOS, it never would have moved or turned faster than minimum sppeds. And the way you describe the differences in TM before and after the reset, is precisely how it would have acted if the above was the case. I'm not calling you a liar on your fan settings in bios, but perhaps there was something you missed that had kept it off or at min speeds unintentionally.
The crazy readings could have been correct. At idle, with minimal fluid and fan movement, at the speeds and voltages you describe, your chip may have still had full TM to play with, and at those exact same fluid and fan speeds, you would see the TM drop to 0, as it would overheat under load quite quickly. 4.2 is a pretty low draw OC, these chips tend to demand massive voltage increase as you go beyond 4.2. On mine, I can actually run 4.2 undervolted from stock at 1.275, but 4.3 requires 1.425v, and 4.5 needs 1.51v to stabilize. Just the nature of the chip, its current stock settings are pretty maxed out when i comes to target TDP and such.
Anyway, it seems you are on your way at least, good luck, and keep cranking away, hah. Worst case scenario, you got a bottom bin piece of silicon, and 4.2 is your actual max. Even at 4.2, you will see some pretty solid gaming performance compared to stock.