Temperature Variations in Primary

I made my first recipe this weekend, a St. Arnold's amber ale. Everything went pretty smoothly (except for using an electric stove and taking an extra hour just to get to the boiling point).

Its in the primary right now, I just started seeing some bubbling today, about 40 hours after brewing. My main concern is the temperature swings in the room. I have it in a water bath with some frozen water bottles to keep it around 70. Today when I got home from work I was close to 76 degrees in the water.

Is there a general rule on how much temperature variation the primary can handle? I know I'm a little on the warm side, even at 70, but I'm more concerned if it warms and cools frequently....

When you say "how much variation can the primary handle", are you talking about the vessel or the yeast? I think both will be fine. Obviously, the yeast will become more active and stressed in the high temperatures, but should also chill out when the temps chill. I doubt rising and falling 6 deg will impact the beer more than what the yeast will do for the periods it is at the higher temps. I don't think you're going to kill the yeast or anything.