My partner and I tried the 300 and 600 lumen versions out as part of a testing project for our training LT last year. We cleared a vacant building that had both small and large rooms and is in a hole so it's pitch black inside.
We both felt that more light=better regardless of the situation. Even though it destroys your night vision, we thought that both lights did that and there wasn't an appreciable difference between them. There was a HUGE difference between both of them and the 150 lumen old TLR we have now.
At longer distances we were told that the 300 lumen version was a "focused" beam and the 600 was just a spread out beam. We found that at longer ranges, the increased output of the 600 lumen version overwhelmed any advantage you got out of a focused beam and the spread out beam actually allowed you to see MORE of your target.
In both of our experiences, the amount of light you're shooting into the room/at a perpetrator would be more overwhelming to the opponent than it would be a hinderance to you. We wholeheartedly recommended the 600 lumen version and were overruled by two high ranking members who preferred the 300 lumen version. Because there was no agreement, we're stuck with the 150 lumen version.
All that said, if I were going to spend my own money on a weapon light, 100 times out of 100 it would be the TLR-1 HL (600 lumens). It's a fantastic weapon light.