Check out Synkromotive controllers. I guarantee you will want to belt out more than 500 amps.
I really DONT want to be able to send more than 500 amps since I will most likely build with 144v of 100ah cells. I don't really want the ability to pull more than 5C because I don't want the temptation to suck the life out of the cells.
I am not intending to build a dragster, just a 'decent performer' minimizing cost and maximizing system life. 500amps at 144v to a ADC 9" in a 2000# car will be more than enough for a 50 year old vehicle.