6500k only refers to the color spectrum.
it's not any brighter, it's just 'bluer'....
you can, to tell you the long story short:
photosynthesis is how plants make food. the highest levels of this activity happens when plants are exposed to spectrums of light close to 2700k and 6500k, not in-between.
2700k refers to soft white bulbs, 6500k refers to daylight bulbs. Softwhite bulbs are redder in color, Daylight bulbs have a blue-ish color to them. You want as much of these two color spectrums to hit the plant as possible. It is commonly stated here that 6500k is better for veg, 2700k is better for flower, i don't know how accurate that is, but it is true that these two colors give the plant the most photosynthetic activity.
you can use a mixed spectrum, just add all the bright white lights you have, add 2 26 watt daylights, 2 26 watt softwhites. that will be enough light to last you the whole grow.
and you need a place that's pitch black when in the dark, a light leak might cause a female to hermie....