If you can leave them in there AND use the 2700k ones, well sure, that'll help. If you're asking whether you should buy three 2700k's and three 6500k's, and you want to use six lights for flowering, then no, get six 2700k's. But if you already have some 6500k's laying around that won't be used otherwise, and you can keep your temps under control, throw them in there too!

I don't know that you can really go too overboard in terms of lighting with CFLs for flowering; the more the better. I just packed 500+ watts (real watts) of CFLs in a tiny closet (2 big bulbs, 12 smaller bulbs), and I'm trying to figure out if I can get more in there without tripping a breaker. I'm not even bothering to worry about the spectrum either - I'm just putting every bulb I have laying around in there. I'm hoping I can squeeze another eight bulbs in there, bring it up to 700 watts. Lol, pretty crazy, I know.