Efficiency only matters during the often short bulk phase of charging.
Once the absorption voltage is reached the efficiency does not matter because you have excess power.
Loss of efficiency during bulk will usually be made up by the MPPT function over PWM. Yes if you have 90v in series vs 3x 30v in parallel both through MPPT your efficiency will drop a bit with higher voltage. But again it only matters during Bulk.
That is probably the hard part is comparing the higher vs lower MPPT and separately comparing parallel PWM to MPPT. Several variables in play at the same time.
All a moot point until you actually choose a wattage and start building a system.
