Depends on your body type/bone structure. Mike Tyson and Oscar DeLahoya are about the same height but Mike would have to die and decompose for a few months before he could be 165 lbs. and Oscar would be a butterball at 225lbs.
Since you are asking this question I take it that you are probably out of shape and not carrying the 225 well. To find your optimum weight I suggest gradually dropping weight by training. Monitor your weight, keep going down until you feel weaker and you do not have the same energy that you had before. This is when you dropped to low. Add lbs. back slowly until your energy and strength return. Thats when you're there.
You need to know your body, and only you will know at what weight you feel best (what ever weight that turns out to be ). Do not aim for a particular weight, take it off 1 lb.at a time and feel it out. Do this correctly and you will not lose much power if any.

Good Luck.