I sailed my FC all over for 16 years without an engine. I would have to agree with you on the thought that she needed a little more ballast. But for the most part it just remained a thought.
Probably the largest improvement in her sailing qualities happened right around the time I took 350lbs out of her bow. WOW, what a difference. She would pick up and beat to weather like a bat out of hell.
Also, on my BCC I have rigged her with synthetic rope rigging. This took almost 70lbs aloft out. That has made a big difference for my BCC. I was able to carry full main and yankee in 20kts of wind, beating to weather, "just" burying the rail. Couldn't do that before.
So I would check your weights, and take weight aloft out first. As it sounds like you have already discovered the benefits. They say to figure a factor of ten for aloft vs ballast (rough estimate). So if you can remove 40lbs aloft, that would be roughly equal to adding 400 lbs in your keel.
In the back of my mind I was always worried about upsetting her sailing qualities by going outside what Lyle had designed. so I made sure she was properly set up first as far as trim and weights.
One last thing to consider. It takes sailing power to beat into a gale. I don't think the FC is a large enough boat to develop the power to beat into a big wind and sea. Believe me when I say I have tried. No doubt she does really well considering her size. She just needs to be handled a little differently because she is a "small" boat. So you just need to heave to earlier than a larger boat.
US Virgin Islands