Is the bass more slamming in the 250 and 600 ohm variations?
No, you just need more voltage for higher impedance headphones.
In power efficiency there is no big difference between the various impedances.
It is a relic from the old days because headphones in the old days were connected directly to speaker outputs.
With the modern low voltage devices came lower impedance headphones which require much less voltage to play equally loud.
In the case of the DT770 (32, 80 and 250 Ohm) there are not only differences in voicecoil impedance but the driver differs so the 250 Ohm does not have the same response as the 32 Ohm.