sharkneto is one of my top favs off the top of my head. Their latest completed Viktor and Five-centric fic 'sometimes age comes alone' is about Five aging himself badly, and it's got some really great moments between them.

And one of the best if you want a novel, Holding It Together is massively great. They went back and reedited the entire thing to switch to Viktor's name after it was announced for S3. Writes Five better than I ever could, but very inspiring to me!