I would venture genetics play a part in this, not to mention body structure, limb length, etc. But based on observation I'd say it's possible but only to a certain few. If your focused on Strength and Conditioning I wouldn't focus on size. Especially if your doing MMA along with rugby.
Whatever weight you feel best at should be your qualifier. Plus when you determine your fighting weight you might be surprised at how much strength you maintain or even re-gain.
I'm 5'10 and I was a lean 210 when I first started Muay Thai and BJJ. I'm currently 192 and I still can hit most if not all my max lifts, with some signs of actually breaking some old records.
So don't associate too much of your strength to your weight, yes it's a factor but it's not the end all for every person. Now you have different genetics then I do and you may find you can maintain 265 and keep truckin, in which case I say congrats and I hate you ; )
Ultimately I would advise that you eat smart, traing right, get as strong and conditioned as you can be healthywise, and let the bodyweight cards fall where they lay. Because the pounding your body is going to take from MMA and rugby, both I can quote from experience, will be more than enough punishment, trust.