Kind of hard to say what your efficiency was since I don't know the gravity contribution of the graham crackers. I would say you were probably somewhere in the mid to high 70's. To determine your efficiency, you need to know what the maximum gravity contribution is for the grains you are using. For this task, I use a table in Palmer's "How to Brew" which lists the approximate max points you will get from each grain. Then you just do the math. For instance, you had a pre boil gravity of 1.047 and a volume of 6.5 gallons. That's 47 x 6.5 = 305 points. Here are the max points for the grains you used. 2-row - 38 PPG, 80L - 34 PPG, Choc Malt - 28 PPG, Graham Crackers - Unknown. If the crackers didn't contribute any sugar (which I'm sure they do) you could easily determine your efficiency as follows.
Max points = 9 * 38 + (8/16) * 34 + (4/16) *28 = 366 points per LB per gallon. You ended up with 305 points so 305/366 = ~ 83% efficiency. That is actually lower, of course, since we don't know how many points the crackers contributed.
Hope that helps.