The RP series have super high sensitivity but you know that already. Even if you subtract 6 dB from their specified numbers to allow for marketing hype and perhaps some exaggeration in their nominal impedance, they would still end up with sensitivity in the neighborhood of 90 dB/1W/1m. So unless your room is really big and you must listen to reference or higher levels, more amplifier power won't improve sound quality for you.
If you do need more power for those reasons, the A300 won't make much difference at all, you should probably be looking to the pro amps such as those made by QSC and Crown audios. In fact if you are determined to get the A300, I would suggest you use it for the other channels and leave the L/R mains with the RX-A3060 for it's better dynamic capability for hifi stereo enjoyment.
I am sure a lot of people can hear the difference between DACs but in theory even the RX-A1050's ES9006A has specs that are far superior to any high end preamps/amps so unless there are other reasons behind the scene, I doubt the upgrade to the ES9016S would make an audible difference. Regardless, if I were to get a Yamaha I would definitely go for the 3060 because of the higher end DAC but that's just me. I have quite a few DACs and is about to get another one, the Oppo Sonica, but I honestly cannot say one sounds better than the other.
So for practical value, the RX-A2050, A2060 are probably better but to me the 3060 is still the best choice for people who can spare a few hundred dollars more. Now, the CX5100 uses ES9016S for even the surround channels, that to me is too much, what a waste..