Help choosing a new Telephoto Zoom

Hey Guys,
I currently have a Sigma 70-300 that I first purchased along with my Rebel 2000. I am really thinking it is time to upgrade this lens to something with IS. I first considered replacing it with a newer 70-300, but I have decided that I have a little more money to spend for this glass. I know that this question is asked once a week, but I feel like I need to ask myself.

So here are my options.

The Canon 70-200 F4L IS + the 1.4TC With the mind to buy a 100-400 much later.
The Sigma 70-200 F2.8 OS + a 2xTC (Sigma) with the idea that I might be able to upgrade to the Canon 2.8 SOMEDAY

I like the idea of the Sigma for a couple of reasons. I am not one who really wants a white lens just to stand out. I also like the faster shutter speeds that 2.8 will give me for stoping motion (kids). I also like the ability to extend my current FL all the way to 400 instead of just 300 (well, 280). These two options both cost the same amount, but I am thinking the Sigma might serve me for longer. I am concerned about AF speed of the Sigma both with and without the TC.

So, anyone got any suggestions?

I'm not sure that you are going to be happy with the 2x regardless of what lens you put it on. The aversion to white lenses is a silly consideration. I love my canon f4IS, and I have no experience with the sigma. The canon is canon's second sharpest zoom lens and is a well built machine.

What are you going to shoot with the lens? Outdoor sports, indoor sports, portraits, general wildlife, birds? The best choice will depend on the application.

I am planning to use this for a variety of things. I do plan on using tis for both wildlife and some birds. However, kids make all of the others a distinct possibility. True portaits are probably the least likely. The idea that this will be an action lens is one of the things leaning me toward the 2.8. But it also makes me wonder about autofocus speed.

The 70-200 f/2.8 with a 1.4x TC will cover your action needs plus be useful for some wildlife (using the TC). However, for serious wildlife you will probably want at least 400mm (so the 100-400L), and definitely need at least that for birding. So the primary question should be what is most important to you first?