Check out the specs...
3000 EX-48:
6500 EX-48:
Biggest differences look like...
-Inverter output watts different (3000w vs 6500w).
-Surge power rating (6000w vs 13000w for 5 seconds)
-Number of units possible to parallel stack (12 vs 6)
-Number of PV inputs (1 vs 2)
-Battery to inverter efficiency (94% vs 90%)
-PV to inverter efficiency (97% vs 93%)
"Any benefit going with the EG4 6.5 vs the 3kW?"
-Wall space when stacking, including airflow space required between units, overall mounting footprint (depending on how many you expanded to in the future)?
-Less input and output breakers required (if using larger unit) when stacking multiple units to get same power...
-Inverter/charger efficiency differences...
Note:
Both models require minimum x2 units to get 240v/120v split-phase output.
Hope it helps...