I used an XTi for most of my early DSLR shooting, even buying a second one that I kept for a while, before a 40D displaced it. That first XTi remains, having reverted to being a shared family camera. Yes, in good light, it still does quite well, but in low light, there are better alternatives.
For a good read on low-light shooting, Zack Arias's Tumblr site has an article, "Low Light Blues," that should become evident with an internet search. (This iPad is not very good for copying and pasting.) Even better, follow the Cameralabs support link to Amazon, and order either the physical or Kindle edition of Zack's book, in which a chapter expands upon his Tumblr post, and specifically addresses low-light images being found slightly out-of-focus. His terminology is very non-technical; easy to understand.
I know very little about the 70D, so cannot be helpful in that regard. When I saw it replicated the ergonomics and controls of the 60D, I lost interest. The superb ergonomics of the 7D was one of two factors that firmly established me as a Canon DSLR shooter, rather than buying a D300s, which my wife was using at the time. (The other factor was my first high-end lens acquisition, an EF 100mm 2.8L Macro IS.)
To be clear, I am not saying the 70D is a bad camera!
My long, skinny hands prefer the hand-filling grips and heft of the semi-pro/pro 7D bodies, to balance heavy lenses while I shoot one-handed at night, as my left hand is often holding an off-camera LED light/torch or Speedlite, and cannot support the weight of the lens.
I do hope that some of the 70D's AF technology, along with some a the 6D's low-light AF capability, trickles into a 7D successor!