For good CFL growth you DO want to add up lumens but keep in mind your CRI rating is much higher so your color rendering is far superior to an HPS or MH lamp. What your going to lack in is lumens per watt. You will never beat out an HPS or MH lamp for lumens using CFL's but you will be able to keep the lights MUCH closer then you would with an HPS or MH, therefore your lumen output directly to the plants will be similar. There is something to be said for growth lacking toward the end when using CFL's and my only conclusion for that is plants use more spectrum then a set of 2700k CFL's are going to produce.
I would love to see someone do a comparison with a light meter using a 400w HPS and 50,000 lumens of flourescent in a 2' x 3' area.
My best suggestion would be to go with a mixture in flowering. If you were using 16 200 watt CFL's, in 2 homemade reflectors made from oven trays, you could get potentially 160,000 lumens and about 3,000 watts. You could get the same output from a 1000 watt HPS.
In conclusion, for stealth or small grows where heat can be an issue, flourescents are a good solution. You can cram 30,000 - 40,000 lumens of flourescent light into a 1.5 square foot area while keeping heat really low. If you want a larger area you should really go with an HPS and supplement with compact CFL's.