More whiter does not mean more bright even on human eyes it may looks "brighter".
The brighter is measure by lumen, in my memory the 4300k is the brightest across the range, 6000k is a little bit lower in lumen(cross the same brand),but consider it is more whiter, so it looks more birght, it get a very good balance between lumen and temperture, that is why most is people go for it.
Phillip oem d2r 4300k have 3200 lumen
Phillip oem d2r 6000k have 2400 lumen.
I dont trust other small brank who claim their 6000k have 4200 lumen like this: http://www.omegaxenon.com/index.html
just for your reference