You know the feeling of yanking a daggerboard out of the trunk of a dinghy, the whole world changes? Not so with a good sized sailboat with a stub keel and centerboard. There are many boats that sail with a 4' keel stub or full keel, and no centerboard. The simple difference is, they don't sail as well to windward as the same keel with a centerboard.

You can sail the keel centerboard boat just as well(it will feel the same as Chris said), with the board up, it will point and go to windward, but it won't point as high to windward. Determining that difference to windward in a keel/centerboard, isn't easy. I've talked to quite a few people that can't tell if their centerboard is up, or down. That's understandable, the boat doesn't feel much different either way.

The difference will be either subtle or apparent in different conditions, in how high the boat is pointing. I find the change easiest to see in watching a gps track average - gain windward degrees as the board is deployed. It may be as much as 5 to 10 degrees in my boat, or in some conditions, undetectable. But like that daggerboard in the dinghy, lift happens when a plate is lowered, same as your hand rises out a car window when you flatten your fingers, and attach the wind to it.

Other indicators are your wake. As the board is lowered, the boat slides less to leeward and consequently, the wake diminishes in width. From there, the fun begins as you can be subjective with your own boat. When windward pointing increases, so may speed. The dynamics of sailtrim with the board increase, and so on.

I'm sad your lake conditions are doing this to you, Craig. If it weren't that you own a great boat you love, I'd recommend a keel centerboard for you situation(on the other hand, I wish we could keep the water in your lake). I hope you get it sorted out.