Three inches and your running serious risk even with proper air flow. You are right in what you say about stretching but thats why you pinch and trim. 8-12 inches is ideal for CFL's. I've developed a 3 month system with a really good yield. I tried the whole close as possible thing but found I just kept running into problems. The humidity in a room can drop completely in 3 minutes. Say your out for a few hours? One day you might regret being impatient and putting them as close as possible. I understand that it may sound absurd but they should not be any closer than 5 inches if you dont plan on not checking up on them every couple of hours. It could be very true that closer is better but most of the people saying that are probably extremely experienced growers. I wouldnt advise someone whose still asking questions and not completely comftorble to push their setup and plants to their limits.