yeah you can mix the spectrum. it's one of the benefits of floro lighting. if your plants are more than 10'' tall i would reccomend some side lighting. a few cfls or t5 strips on the sides will make a major difference in your yeild. when i flowered with t5 i had about 70% bloom spectrum and 30% cool veg spectrum between all the lights. i would reccomend a bit of a higher ratio of warm to cool lights, but 50/50 will work fine.