Hi Cory,
I figured I would chime in here too even though I am no expert. I have owned the Rebel T1i though, and currently have both the 6D and the 70D. With the Halloween coupon that was available for the Refurbished 6D, I purchased that at a little over $1,200 as I could not pass it up. Not sure if something like that will come up again for black Friday or during the holidays, but if you do not mind refurbished I think it is a fantastic buy.
Of the 70D/6D I agree that the 6D is the camera to go with. Even though both are 20mp sensors, the images I get on the 6D are substantially better, especially at high ISO. I personally tried to avoid the T1i going over ISO 800. If I recall it didn’t have 1/3 stop ISO adjustments or auto ISO so I tended to not want to place it at 1600. Now I tend to shoot in manual mode setting the shutter and aperture how I want it and letting the camera pick the ISO for me (I do wish you could bias the exposure when you need to which you cannot, so sometimes I’ll shoot in Av or Tv instead, or change settings manually). I feel that I get a good 3 stop advantage over the T1i with the 6D as I’ll easily let it go up to ISO 6400. I personally think the metering and auto ISO implementation allow me to work much more quickly than I used to with the Rebel. I haven’t shot indoor sports, but my indoor very active toddler gets a lot of pictures taken of her in quickly varying low light conditions. As long as I am using the center point it does a great job. The other focus points aren’t too bad provided the lighting is better.
What I really like the 70D for is the frame rate and buffer. Neither are quite as good as the 7D I had (the 7D’s buffer in particular is what I really miss with the 6D). I’ll also move the focus point around without thinking much about it, where I usually keep the 6D’s in the center. One other thing I like about the 70D is the video mode. For some spontaneous event (like her trying to summersault) having the video with autofocus and flip out touchscreen is really nice in the 70D. If they just could combine my favorite features of both cameras I’d be all set with one . I’m hoping that will be the 5D Mark IV but until then I’m extremely happy with the 6D (especially since the 70D is technically my wife’s).
I’ve also been really thinking about a fast 35mm lens. I almost bought the Sigma 1.4 refurbished this morning but Sigma was out of stock by the time I came back after dropped my daughter off. Guess I should have jumped first thing. I do have the Canon 50mm 1.4 and use that a lot indoors. There are plenty of times when she is too close and I can’t back up, or I want to get more in frame and the 50mm isn’t wide enough.
Hope this helps. In summary, IMO the 6D is such a better camera that you should be extremely happy taking pictures with it over the Rebel.