This is a constant struggle for me. The good thing I think about being too big/strong is you can always cut back on certain areas and change your focus to speed/endurance. I think this is easier to do then to make your focus size/strength since it takes so long. There are a lot of factors though, if you want to compete and you have a weight class decided, and let’s say you don't even need to cut weight, to make weight for that class. I think it MAY be smart to gain some size. But depending on your strengths, let’s say its speed; you may want to just drop a weight class. I'm talking as if your main priority is MMA.
MMA has became bigger then weight training/bodybuilding for me. But I still love lifting weights. I just have given up all heavy strength training for now. I try not to work shoulders too much anymore; when I do I try to do high reps mainly. They are over developed and my arms get fatigue to hold up for extending periods of time, and the last thing you want to do is drop your hands in a fight because they are getting to heavy to hold up near your chin. Triceps I also rarely train, because of my height jabs are not something I will use often, mainly to set up a hook, but I get very fatigue throwing jabs. I have been as heavy as 240, and 235 was a common weight for me in the past at 5'9". Right now I'm walking around 205lbs 8-9% bf; I have gotten down to 193lbs around 6% bf recently. I felt the best at this weight, but its hard to maintain. I couldn't hit quite as hard but I could throw a lot more punches’ total, which is more important to me. My speed and endurance was great also. For me middle weight 185lbs will always be my goal competition weight and 190-195lbs my Ideal walking weight.