Sigma 70-300 APO DG.... vs Canon 70-200 plus extender

I currently have the Sigma 70-300 f/4.0 for shooting soccer but I'd like to get a faster lens like the 70-200 f/2.8 but I'm often shooting beyond the 200mm focal length. Would it be smart of me to get the 70-200 and then an extender or would that be a waste of money on my part? I can't remember what I have read about the extenders and what they take away from the shot. Can some fill me in?

Thanks,
Karman

tthe 1.4x tc will take one stop of light away (making it an F4) and a slight bit of sharpness. i have used this combo, and it works very well. but if you think you need the reach more than the extra Fstop, you might look at the sigma 100-300 F4. it can take a converter well form what ive heard too.

Any 7-2 f2.8 lens + 1.4x is going to be better than the Sigma 7-3 at 280mm f5.6. IQ will be better and AF will too. The Sigma 7-3 isn't the ideal "sports" lens but it can suffice for certain situations. I have the Canon 7-2IS, 1-4IS, and the Sigma 1-3EX, and the Sigma is the one I use for soccer and outdoor/daytime sports. You should consider the Sigma 7-2EX with 1.4x or the 1-3EX.

Thanks so much for the advice. I'll start researching and reading.

Karman