I never used that much grain or a keggle, so dont know. You may be fine. I have done 23-25 lbs in a 48qt cooler and still hit mid 70s%, but I had to sparge a little extra and boil longer. If you go that route you could add some hops at say, 90 minutes, and get more IBUs out of them. You may not need as many to bitter that way.