in general .. the more light the better .. so if you can get the 6 6400K for veg and then add 3-6 2700K for flowering ..
6400K provide most color in the blue spectrum which the plant use most of in Veg .. tho a plant use all light all grow .. just more blue in veg and in flowering it will use mostly red/yellow light (2000-3000K) to grow its buds ..
if you only have money/space for 6 bulbs I would mix em up with 3 of each all grow ..