I too have used the small servo's and found I had to add a bunch of weight to the plane to meet the 4.5lbs. One of my planes took 7oz. to be up to weight, I found just using, say DS537's the weight is real close, plus it's a known, ''Work horse'' servo. The most I've ever added after that is 1 to 1.5 oz to the planes.
Gather around kids it's time for more of Uncle Skully's opinions about things. (That no one agree's with)
Ok 2 servos in the wing are for safety, right?,,,, WRONG!! you can put 2 in, in case one fails, you can still fly the plane. What are the chances that it will fail in the center position? VERY LOW. What are the chances that, at race speeds, you will be able to ID a problem, figure it out and correct for it, again VERY LOW. Now this one will get you revved up!! Using 1 servo in the SRM2 wing and it fails, in the center position, and you are able to figure it out and correct for it before a crash, what do you do? My answer is fly it on the rudder, (not race it), try to land it for repairs. IF you are NOT skilled enough to fly and land a plane with rudder and elev. ONLY, you don't need to be out there racing with us.