My next lens investment

not to mention that the 1.4x will make it a f/4 lens and the 2.0x will make it a f/5.6 lens

I tried the Sigma 70-200 with a 2x TC and was extremely disappointed. The 70-200 is a real nice sharp lens by it self, but terrible with a 2x TC.

To get 400mm was my main plan also, but discovered quickly that was not the way to do it and returned both items to the retailer.

i LOVE my sigma 70-200mm...

a picture from last night, low light, no sharpening, only jpeg resize and noise reduction

a fellow shooter had a Sigma 70-200 and a Sigma 2X TC. I thought the images were pretty good. That maybe the way to go if you don't want to spend a grand for a supertelephoto zoom and only occassionally need a 400mm reach.

But considering I already have the canon 75-300 /f4-5.6, wouldn't it really be a waste to get the 1.4 and use it on the sigma?

not if you want a f/4 quality zoom over a lesser sharp cheaper zoom

I would recommend skipping the 2x and get the 1.4x if you want to extend the reach a little. The Sigma with 1.4x at f4 is still much faster and better than the 75-300.

I thank you all for your feedback, if there was some sort of virtual bar, I'd love to buy you all a beer (providing your all of age of consent of course)

yea stay away from the 2x unless you got some of the ultimate glass like the 300 2.8 or the 400 2.8

remember with your rebel the 70-200 is like a 112-320 on a ff

The sigma is a great lens, but I'd suggest get a 1.4 teleconverter instead, a lot of these lenses do a lot less well with a 2 x, but the 1.4 doesn't seem to lose much IQ.

I can't comment on the 2x, but the Sigma 70-200 and 1.4TC is a great combo, and I find that I very rarely want more reach for the stuff I shoot.