I got my set of Gateron Yellows today and wanted to share with those that also had the same question I did.
"What is the difference between the Gateron Yellow and the Gateron Black if they have the same actuation force?"
NOTE: This is just my opinion and I do not claim to be very knowledgeable in this area, so please keep that in mind when reading.
To me, the Black has a little bit more "push-back" or resistance when you're getting closer to bottoming out with the key. This makes it easier to let the key travel back up and makes it feel a little bit heavier than the Yellow, even though they are supposedly the same in actuation force (50g). The Yellow seems to be closer to a Cherry MX Red, but smoother, than it does a Gateron Black.
This is just my suggestion, but if you've tried the Cherry MX Red and feel like you might bottom them out, then I would say you're better off going with the Gateron Black. If, however, you are fine with the Cherry MX Red, but want something a little bit smoother or just so ever slightly heavier (real slight), then I would go with the Gateron Yellows.