i started mine under a 600w no problemo just dont do anything stupid like have the light 10 inches away or something. i think i started mine at about 2 feet and lowered it each day and just monitored them for stress. they took it no problem.
the way i see it is i have always started my outdoor girls in full sun. if they can handle all day full aussie sun they can handle 600w.
that said if u have other options which i didnt why not save on electricity while u can and run cheaper lights.
personal choice really