Ok now you guys have me leaning towards a canon 70d or 7d mark II.
I shoot both indoor and outdoor sports for my kids and their friends.
Things I don't like about the 3ti currently are:
1. To much grain the higher the ISO (low light situations) with a good lens.
2. AF system could definitely be better.
I also have been contemplating getting 85mm 1.8 lens for gym lighting.
The AF system on the 70D is a good leap better than the T3i. The AF system on the 7D mk2 is a quantum leap better than the T3i.
The ISO grain on the 70D is ok at 6400 at least I wasn't as bothered by it as some might. Even up in the 8000 range I was not annoyed by it. But 6400 is a threshold before you have to ask yourself whether you are OK with it or not. Dunno about the 7Dmk2 on this but some say it is slightly better or similar.
In gym lighting an 85 1.8 on crop would probably work fairly well. Fast lenses when I had them on my 70D produced some images that I definitely LOVED especially when I compared to kit lenses. The pictures when used with a Sigma 18-35 1.8 or with a Sigma 50-150 2.8 IMO were WOW (for me anyways) and when I took them into Lightroom my wife always marveled at how images that SOOC she already thought were nice went over the top.
BUT... and I say this ONLY for informational purposes... I ended up selling the whole kit because I kept being annoyed by the low light foibles (And I mean dark! Like the inside an old fashion train car with candle lights dark). The 70D AF's in -0.5EV around that range it is fairly dark and it has issues autofocusing even with a good fast lens attached and finding good points of contras to target. Then most of the indoor events for my kids required higher shutter speeds and bumping ISO, in the end I decided I would prefer full frame to fill those needs and a camera that can do AF at -2EV (5dmk3) or at -3EV (6D with center point or D750 with center column array) made me decided I wanted more... that said the AF system on teh 70D spoiled me so much that the 6D just wasn't going to make me happy... and obviously the other two cameras are a larger price jump.
So if ISO is a true issue you may want to account for that and go 6D. If AF is a bigger deal go with the 70D or 7Dmk2 and be very happy! If you end up wanting both great AF system and better ISO in darker situations be prepared to pony up more dosh to go 5dmk3 or D750.
Best of luck with your decision, can't wait to hear your final decision!