Since the OP mentioned "bulb" lumens and not out the front lumens, which is always lower, the Malkoff MC-e (cool white) is probably as close as you are going to get in a 6P size flashlight or Malkoff's own MD2 using 2 RCR123 batteries. Turning on with 500 out the front lumens is probably as good as your going to get to 600 "bulb" meaning at the source lumens in a small package. Much smaller than the M1X or Solarforce L900M type of lights. Those have more than 600 lumens out the front and that means there "bulb" lumens are well over the minimum he was looking for. Not that its bad, just not the smallest package for the stated starting threshold level.
Don't know of any other commercially available light that will reliably do that in a "smaller" package. Some of the Wolf Eyes lights should do that but are somewhat bigger or have larger heads.
You're quite right in that if the OP really meant bulb lumens, you could go much smaller than if he meant OTF lumens.
However, it seems strange that anyone would be interested in bulb lumens because this is not at all useful in the real world.
The only meaningful measurement of output is out the front lumens.
No point in having a light that "in theory" can output 900 bulb lumens if it only outputs 350 OTF lumens (like many of the Dx clones).
You're quite right in that if the OP really meant bulb lumens, you could go much smaller than if he meant OTF lumens.
However, it seems strange that anyone would be interested in bulb lumens because this is not at all useful in the real world.
The only meaningful measurement of output is out the front lumens.
No point in having a light that "in theory" can output 900 bulb lumens if it only outputs 350 OTF lumens (like many of the Dx clones).
I would think that the smallest MC-E light that genuinely puts out over 600 lumens is probably the O-light M30 Triton without the cell extender.
ie. 3CR123s or 2 18500s.
Given the very impressive output on high, this is still a relatively compact light.
I think its probably another level on in brightness compared to all the Dx clones, the P60-sized lights and also the WE MC Explorer.