This was your stated goal: "I am about to start a family so I envision this lens being used for: vacations, sporting events, general purpose."
Starting a family could mean anything, but I read it as "I'm about to get married and/or have a baby." If that's the case, I think it's probably time to replace your eight-year-old camera. Having something with good lowlight performance is really helpful with baby pictures. I think it's time to replace your XTi.
While a 70-200mm lens is really helpful for sporting events, I don't see it being very useful for vacations or general purpose photography. I think a 6D + 24-105mm would be a much better choice, and if you sold your other stuff, you could get that combo for "only" $1200 out of your pocket.
You read the goal properly. I get married in May and envision having children shortly (within a year or so) thereafter.
I've admitted that I want to replace my XTi and get the 70D after my visit to the photo store yesterday. See Post #40.
I find my 17-55mm lens perfect for what I use it for. I now envision a need for something to go beyond it, and 'complete' a good two lens combo......basically covering 17mm-200mm. I doubt I'd miss the 55mm-70mm range. I am fairly set on my choice at this point. I will purchase the camera body first, then when kid(s) do arrive, I will look into getting the 70-200.
The 6D + 24-105L combo @ B&H is $2,199. Not sure where you are getting $1,200? Anyways, I looked into the 24-105L prior to getting my 17-55mm lens. I chose the 17-55 since it was f/2.8. I don't use my flash much, so this was a good lens for snapshots with lower lighting levels.