The most I've gotten is 492, but I wasn't playing alone; I teamed up with a friend and we defeated 6 opponents (in an alliance) at 200%, and we finished in 56 turns. When I played alone, the maximum I scored was around 462 against 7 opponents (in an alliance), but often I only got 442-449. In all cases, this resulted in the "Archangel" rank. Of course, this was all done with the City Portal and Dimension Door.
Maybe someone knows, and if so, could you enlighten me? I've been playing for about 10 years, and I still don't know. And if it's not too much trouble, could you tell me what timeframe I need to aim for and what I need to do? Maybe I'm missing something...