Looks like a fun trip to clear lake :) You can never be sure on those big mystery breakoffs but I have hooked quite a few big cats while fishing for bass and what you described sounded pretty catfish like. The cats usually start moving off slowly when you hook them and take a few seconds to come alive. Then they start running and they stay close ot the bottom. They also give big twisting headshakes as they get more pissed off.

Sometimes a fish fools you, like the 13lb cat I caught once on a 1oz rattle trap. I thought for sure I had a 15lb bass on. Or the other weekend at the delta I hooked a 5lb bass on 8lb test and it ran me like a foul hooked carp and never jumped for probably 2-3 mintues. So you never know, maybe you hooked one of the elusive 10lbers of clear lake :) That's the fun of fishin.