70-200 2.8/IS, 4/IS, 2.8/PRIME I'm so lost!

I know I've been going back and forth between the 200/2.8 prim, 70-200/4 IS, and now I'm thinking the added $$$ on the 2.8 IS will be well served. I grabbed the 200/2.8L for the speed and to fill in the missing focal length. Now, I find I need a tele zoom (sold my 70-300 before using it to grab something fast). Well, I still have the need.. the need for speed. I also need IS (I know I need it, no sense setting up a tripod in a dental office where space is prime real estate for treatment rooms instead). In my office, we take portraits of patients who have extensive work done, so this lens will be used in that setting and be a business expense... BUT I'm not entirely sure I should do it.

I've searched ALLLLL THREADS comparing the f/4 IS vs f/2.8 IS for pros and cons.

PLEASE HELP ME! (is $1485 shipped a good price on a 70-200 2.8L IS? anyone wanna buy my 200/2.8 Prime?)

PS, I really started thinking about the 70-200 2.8 today during faculty photos, and after seeing the photographer use it I got the itch.

... Although I have the 70-200IS2.8 and recommend it highly as a zoom-tele, I looked at your gear list and would recommend the 24-70L2.8 instead. From your post, it sounds like you are looking for a fast zoom that will produce high IQ for patient dental pics. ... Anything beyond 70mm on your 40D would be pretty long for shooting INSIDE your dental office. But the 24-70L will afford you the high IQ you are looking for, and will reach up to 70mm for you to get close/tight shots for detailed images. ... Just a thought.

well, i shoot at 200 quite a bit (outdoor portraits, albeit), so that's why I've been looking into the 70-200. It'd give me more freedom above 50mm. For shorter portraits, I break out the 50/1.4 or the 100mm macro (this is usually lens of choice in my office chairside due to my intraoral shots).