Question about CFL physical size

So, I was perusing amazon for my flowering bulbs and I came across this bulb.

http://www.amazon.com/Earthmate-EP4052AE-40-Watt-Spiral-6-Pack/dp/B001WAL1P0/ref=sr_1_61?ie=UTF8&s=hi&qid=1247627338&sr=1-61

Seems to be a 'low pro' type bulb. Does the actual surface area of the bulb make a difference on bulb performance for a grow, or is it just the lumen output?

I've got a bunch of "low-profile" CFLs. They appear just barely brighter then higher profile CFLs of the same wattage, rated for a slightly higher lumen output too. Cheaper too. For small CFLs, I think the low profile type are supposed to be a bit more efficient.

You should always look at the lumen output rather than surface area......if surface area mattered than hps bulbs wouldn't be worth a crap due to their reletively small size. The low-profile cfl's are nice because you can put many of them in a small area making the lumens available to the plant rather high while keeping energy consumption low.

You should actually figure out the lumens per watt....that will show you the most efficient bulb