3. "Everything else" (as you call it). Governed by Part 15.249. The *average* Tx power is limited to no more than -1.12Dbm (roughly 0.77mw) and can have a *peak* of no more than 18.9dbm (about 78mw). Here's the rub: to calculate the average power using the rules of Part 15.249, you must determine what the worst possible duty cycle will ever be over a 100ms window. Applying a duty cycle correction factor based on that worst case duty cycle to the Peak Power yields a number which must be no more than -1.12dbm. So, the way I see it, you must either guarantee a very short worst-case duty cycle, or else your peak Tx power must be low, or some combination of both. Maybe there exist applications where the RFM69x can easily operate within those constraints, but if so, it's not intuitively obvious to me what they all might be. Speaking generally, the Part 15.249 rules don't appear to leave much wiggle room. That said, I suppose there's a chance you might get lucky when it comes to fitting your application within those constraints. For instance, maybe operating the RFM69 at a high bitrate while transmitting only a single very short packet (with, say, a 100ms rest interval between packets) might get you in or near the ballpark while still allowing a relatively high Tx power. Returning to my OP (above) and perhaps answering my own question, maybe the RFM69HW might outshine the RFM69W in that scenario and prove its worth all while maintaining compliance with the relevant FCC rules.
Closing the loop on the OP and putting numbers on this: assuming my math is right and assuming I haven't overlooked some other restriction, then wrt 15.249 it appears that as long as an RFM69HW does not exceed a peak transmit power of 18.9dbm, it could have a duty cycle as high as 10% at 18.9dbm, provided it does not Tx more than 10ms during any 100ms time interval. That's good news, as that should be easily manageable at higher bitrates.
Unless I'm mistaken, 15.249 does not imposes any minimum bandwidth requirements. Therefore, to pin down the other end of the range, the final step would be to compute minimum bitrate based on minimum packet size, and that would dictate the minimum bandwidth from the picklist. Obviously, lower peak Tx power would allow longer duty cycles.
It would be great if someone besides just me would read 15.249 and run the numbers independently so as to either confirm or refute.
Wrt to 433Mhz, I get the impression that it is legal to use the band, provided the applicable Tx power and duty cycle requirements are met for the equipment's applicable category of intended use. IIRC, in addition there's a minimum wait of either 10 or 20 seconds (?) between transmissions in the 433Mhz band for non-privledged uses, but for a lot of applications (e.g. temperature sensors) that would also be easily manageable. I do think it's worth looking into.