XHP70.2 has really high efficacy, you can get the Acebeam K30 or some kind of 3xXHP70.2 light and have relatively little heat and drain on the batteries when outputting around 2000 lumens. If you want the absolute best efficiency at around 2-3k lumen output, you can grab an Acebeam X80GT— with its 18 XHP50.2s, 2-3k lumen is like a low mode to it.
On a more budget oriented note, Haikelite and Q8 are good options.
Purely objectively, 4x18650 is a much better format than 3x18650 (3x18650 is only 75% the power available while still 87% the handle circumference).
However, I feel 3x18650 is a goldilocks size for ergonomics. I have average-above average sized hands, and 4x18650 tubes are a little too big for my liking, while 3x18650 is much more holdable.