That's actually a very hard question to answer. How much noise is too much noise? There's colour noise and lum noise. Will the image be severely cropped and/or printed 30x40 or mostly 8x10,12? How much detail loss is too much?
OK, beyond all the variables you need to consider, I'd say that I've gotten decent results at 800 to 1600 and will push to 3200 for a few shots depending on subject matter and output. Noise doesn't show up in a print so much but loss of detail is the issue. Get a good exposure, and be careful in post especially with any NR software you may use and you'll be fine. And don't forget it also depends on the subject matter. If you're filling the frame with the Bride's head and you truly want every hair to pop out at you, then you may want to rethink things. A wide shot of the church's interior is something else again. YMMV
If you truly want to know for yourself what's acceptable or not (rather than just reading what I or anyone else can guess at what you do think is acceptable), then go beg/borrow/rent a 7D for a few days and shoot away. No matter how many replies you get here, that's the only way you'll know for sure.