I am fortunate to own and have owned both SxS and OU double rifles. I do not buy the old saw, that an OU double takes much longer to reload than a SxS. It isn't true of shotguns and it isn't true of double rifles. Yes the barrels drop a bit farther, but give me a break. I would love to see a timed four shot string. The English perfected the SxS rifle while the OU was far more common on the continent. The English rifles were used far more for DG in East Africa, but that doesn't make the concept inherently better. I do believe, that the OU rifle is much easier to scope than a SxS, and more likely to give good results at longer ranges than its SxS cousin when so scoped. But when done right, they are both wonderful things.
Red Leg I too have owned and still own both O/U and S/S rifles and shotguns, and unless you are loading both one barrel at a time the O/U is definitely slower to reload than a S/S.
I reload both barrels simultaneously on my S/S doubles and the O/U requires loading one barrel at a time because of it's stacked configuration.
As posted earlier the picture above and to the left of this post it is plane to see the method of simultaneously loading both barrels on the S/S. This does not work on the O/U, and the reloading a shotgun, S/S or O/U, has nothing to do with proper speed loading of a double rifle!
You say you would like to see a timed shoot! We have timed shoots every year with all types of rifles being shot simultaneously, with each shooter being individually timed by a digital timer, and the targets individually scored for accuracy.
In this shoot the bolt rifles are loaded with one in the chamber and 3 down. The doubles are loaded with one in each chamber and the double must be reloaded after the first two are fired while the bolt and lever rifles have only to work the bolt or lever 3 times. The timing starts for each shooter when he fires his first shot, and stops when he fires shot four. The targets are then scored. The target is an 8 inch bull with a 2 inch ten ring. The highest possible score is 40 points if all four bullets het the two inch 10 ring.
My last score was 36 out of the possible 40 points, and my time was four seconds flat. The rifle I was firing had a auto safety that had not been disabled which is not the same as all my other double rifles, and I forgot the auto safety, and tried to fire shot 3 with the safety on, and had to disengage the safety and pull the trigger again, and still fire all four shots in four seconds flat, with 36 points of a possible 40 for a perfect score. If I had not forgotten that safety, or been shooting at a charging lion that extra second could have earned me a bad mauling or even death. Fast reloading of a double rifle is certainly a skill one needs to learn.
One more thing, not one lever or bolt rifle came in higher than fifth place out of 40 shooters. I took third place even with the safety screw up!
What I have never seen is a timed string between experienced SxS and OU shooters. 
