worth noting that with impure tabs, takings several doses may bring any active adulterants to a threshold level, polluting the mdma roll. I've seen people transported to a dimension MDMA can never get you to due to munching numerous, adulterated pills.
Frankly, 600mg seems unneccesary, double drop if you want to push your boundaries but beyond that, you wont feel significantly elevated euphoria, physical sideffects will be much more pronounced and as i said adulterants could turn it into an experience you were not expecting. Do what you want of course, but question why you want to take it to these extremes