I had recently started (but haven't yet finished!) a series of "tests" using 12wt and 28wt top threads. When I used 12wt in the bobbin I didn't have any tension issues - but the starts/stops were sooo ugly. I didn't like the look of using 12 in the top and bottom at all. I tried a 50wt (I usually use 60wt in the bobbin) but had the same tension issues that you did. I had similar issues with 12wt in the top and 28wt in the bobbin but not as bad. I tried several top tension settings with all of the above.
I stopped my tests because I had other projects to do ... but yes I kept records of thread weight in top and bottom, needle size, top tension, and the results. I keep my thread in clear plastic sectioned boxes, and I wrote my notes on sticky labels and stuck them to the inside lid where I can see them as soon as I open the box. I also keep my scrap FMQ practice swatches and make notes on them with my perma pen with regard to thread wt's, needle size, and tension. Those are not organized though, I have to look for them if I want one, and I'm sorry to say they could be ANYWHERE - found one in my underwear drawer once. I'm claiming temporary insanity on that one.
At one point I had a problem with my bobbin case and I visited my LQS. While there I talked to a few of them about my issues with 12wt and 28wt thread. Unfortunately neither of them had experience using thread that heavy but both suggested that changing the bobbin tension might be worth a try. As it happens I was buying a new bobbin case anyway (even though mine was still technically working properly it had some wear on the edges so I got a new one), so I'll keep my old bobbin case as the "play" case to try changing the tension on. As I said ... haven't tried it yet as other projects beckon.
Sue