Ah, I have done this.

I have taken at least 10 different flashlights on many occasions to test them out, not withstanding the fact that doing so makes the wife question my sanity. Without question, they perform differently.

It's just like your car's highbeams are useless in fog, that's exactly how a white LED performs. This is why I still carry a yellowish Xenon light with me. I have some red LED lights which preserve night vision and are perfect for looking at star charts (the Proton is my favorite). And I have lights with a lot of throw and other lights with a lot of spill that illuminate fields but aren't very useful for navigating. Some are too heavy to be practical and are some are too light to have any real battery capacity. I like wide lights with spill for dog walking (which I do for half an hour every night), so I can find her if she runs off to sniff something without my yelling for her. Highly focused beams aren't very helpful for that.

So, I always test my flashlights, as I do all my gear. I can't say I'm a huge fan of the "bang the light on concrete" test that so many people seem to love, but I do like knowing how well everything works.