How fast does a Generator Charge your battery bank?

I would not charge the battery packs at more then about 50-55A each.  You will not have perfect matching of the six parallel packs.  I would expect about a 10-20% variance in current between the six parallel packs and will likely get worse over battery aging. 

Each XW+ should be capable of about 120-130A at average voltage during charging of 3.35v x16 = 53.6vdc based on wattage limit of XW+'s  So you will be limited by two XW+'s for charge current max of 240-260A, giving an average of 40-45 amps per battery pack.

80% capacity recharge needs 84 AH x 6 = 504 AH's.  504AH / 250A = 2+ hours.  If you take to full charge, 3.65v x 16 = 58.4v, you will have about hour and half to two hours of current taper off time once you get to 58.4v absorb voltage.   XW+'s should exit absorb when current drops to 25-30 amps for each unit ( 50-60 amp net charge current).  Overall I would expect 2.5 to 3.5 hours to replace 80% DOD.

If you float long term, set XW+ float to 3.35v x 16 = 53.6v.  That still will give you over 95% SOC and reduces excessive SEI layer thickening rate on LFP cells which will increases their internal impedance and eat up available lithium that reduces capacity.  Try to set XW+'s LBCO so XW+'s shut down first on low battery, not the battery's BMS under voltage shutdown.  Sometimes that is tough due to battery cable resistance votlage drop with heavy inverter loads prematurely tripping inverter's LBCO.

Gen fuel consumption will be efficient with 13kW loading although you might consider having ability to use excess power capability for water heating or air conditioner during charging time.

Something to be aware of is the charge controllers also have the potential to feed current a sudden clear break during an overcast day whilst inverter charging which could exceed the maximum charging current, the cumulative total of both. This is something I discovered personally whilst testing, fortunately I was able to shut the generator disconnect off as soon as I realized the sharp increase in current. Below is an excerpt fom the attached pdf which mentions this, they are referring to the 60 150 controllers in this case 



A practical way to avoid this is to only use generator charging when there is no sun, I choose evenings because it's almost guaranteed to clear up if done in the morning and I never charge more than what is needed to get me through 24 hours. This is particularly important when AGS is incorporated.