Didn't you have the T2i before? If you did, how do you think the focus on the 6D compares to the focus on the T2i?
Everybody's getting all hung up on the focus on the 6D. It's better than ANYTHING was 3 years ago (That pretty much covers the T2i.). It's not a MkIII, nor is it intended to be. It's not a DX either, but I'm not a DX or MkIII type photographer. I've never had the focus points on the 6D get
in my way. The 70D has more, yes; but the reason I pick up the 70D is for reach, not focus.
As far as size v. the T2i, you might as well
get over it. ANY of these cameras is going to be bigger than the Rebels. It's by design. I actually like the larger format because it gives me more to hold on to and it gives more real estate for controls so they are not too close together to actually use. the weight's going to be in your glass, not the camera. Thought the semi-pros do weigh more, it's not significantly different than the Rebels to me.
You are going to take a hit on your glass. EF glass is WAY more expensive, but if you do make the move to FF, you will never look back. I do like the option of having the best of both worlds because I can reach for the 70D when I want reach.
I will say this. If you buy the 6D with the 24-105 bundle, you're likely to not really
need anything else except a 70-200 f4 IS, even though I bought the 2.8. Remember this is FF, and the extra stop is gained back by that. That 24 is also a real 24 and not a 36 (or whatever) so that's pretty wide at the wide end.
I still have all my EF-S glass and don't really
want for anything for the 6D. Eventually, I want to get a nice 35 or 28 prime for it that stops down to 1.4 or so just for dark rides at Disney, but I'm not losing any sleep over it.
I could really be very happy with exactly what I have now. It's just not my nature not to constantly be looking for something new to play with.