question

It depends. If there are low to no ac loads while charging then no it will not benefit you anything. However if you are running high AC loads such as air conditioning while charging, then yes you would benefit during bulk phase when the batteries are accepting the full output of the charger. Also pay attention to the maximum rated charging capacity of the batteries, but at 900ah bank size I doubt you are anywhere under the 120 amp output of the charger.

There is also a voltage difference: 50 amp shore power is two legs of 120 volts with 240 (or 208) between them. 30 amp shore power is a single leg of 120 volts. Accommodating the 120/240 shore power requires some additional thought and possibly a second inverter to fully utilize that power. Using 30 amps, you get 3600 watts of usable power, 50 amps 120/240 gives you 12,000 watts (6,000 watts per leg).

If you go with a split phase power system, you also need to figure out how to handle single leg 30 amp shore power when that is all that is available.

Of course, you can always use just one leg of the 120/240 split phase shore power and make use of the additional 2,600 watts.

Sounds like more complicated/work than it’s worth. I’m going to stick with 30a like I had planned. Thank you both for sharing your insight.

If all you are after is additional charging current, there is a simpler solution: use a second AC input to the RV that runs a separate AC-DC charger. You'd plug this in to the pedestal, probably to the 20-amp receptacle. You can get Victron chargers that output up to 50 amps at 12 volts and these could be paralleled -- up to 3 in parallel from of one 20 amp 120 volt AC circuit for a total of about 150 amps or 1,800 watts of charging.