If you put in ceiling speakers in less than in inch away from any framing you can have problems with the dog ears.
I would keep the speakers at least a foot away from the lights. This will keep any interferences to a minimum and even more importantly it will look better. If the speaker wire is fastened above the can lights with zip ties or whatever you will have a hard time pulling the wires over to your hole if its too far away although im sure your keeping that in mind. If you can get in the attic I would just go up there and see what you got to work with before cutting in any holes.
A couple tips I can give you that I have found work well are when you get the cutting template. Get a very small screwdriver and poke it right through the peice of cardboard in the dead center (or close enough. Verify by spinning it and seeing how much it wobbles) Then instead of trying to figure out if your putting them in the right spot just mark out where you want the center to be and then poke the screwdriver right into the drywall. It will hold your template there while you trace around it.
Then once you have the circle traced out take the screwdriver out of the middle of the template and poke it through the drywall in a cross type pattern every inch or so to verify there is no framing behind your hole. (small screwdriver holes are much easier to patch than a 7 inch hole
If your trying to line speakers in a row with can lights or something and dont have anything to get good measurements off of you can pull a string from the center of one light to the center of the other then you instantly have the center of where your speakers need to be. (You can tape the string with some blue painters tape if you cant put a small screw or nail in the drywall.)
Also make sure your dog ears on the back of the speaker are loose before you go to mount it or else it can tighten down on itself instead of flipping out and tightening down on the drywall like its supposed to.
