If your doing this to increase strength, you should really consider doing the 5x5 method, which means you do 5 sets of 5 reps each press..soo you should boost your bench pressing up a little more if your RM is 120..because mines 115 and I train with 95. Also train with 80%-90% of your max for getting stronger..60%-70% to get stronger/toner and 40%-50% for toning...but what your doing is fine if its for getting stronger and toned for the same time..
try looking at bodybuilding.com, best site ever if you wanted to find out how to get stronger..