Almost all CFLs are in the 65-75 lumens per watt area, and it doesn't seem to be improving much or soon. I think 75 is the upper barrier for CFLs; it may get to 80. You're right...T5s are more efficient. I've heard of them getting 90 or even a little more lumens per watt.

But once you get to a 250w HPS, you're going to get at least 100 lumens per watt. The difference between 70 and 100 doesn't sound like much, but it is. To cover a 5 sq. ft. area, you can use one 250w HPS. Or you can use about 360 watts of CFLs. CFLs are great for grows in less than 3 or 4 sq. ft. Once you get to 5 sq. ft. and above, HPS (or T5, I guess) is just better.

Thing is, a lot of people do grow in 4 sq. ft. or less, and CFLs will do a great, great job in situations like that with a minimum of hassle or start up costs.