Minor dilemma - 6D or...

I shoot landscapes, events (not weddings) and real-estate interiors often in low light. I use the original 5D and 40D. I passed on the 5D2 and 5D3 for budgetary reasons but need a high sensitivity sensor. For UWA I use the 17-40.

Choice - should I wait for the 6D @ $2100 or buy the t4i (Rebel 650) now + Sigma 8-16 (12-25 equiv) which has gotten good reviews for total of $1500 or so. The t4i has almost as large a sensor at 18MP and thus a higher pixel density than the 6D. It also has a built-in flash which I like for gentle fill flash when I don't want to bother with my flash gun.

I have thought about the 5D2 but it's 4 years old and I would prefer new.