Mike, for sheer performance on a flat carpet, the Royal beats the sebo into a cocked hat. However the drawback is, it's a dedicated upright - you can get a kit to use it with a pipe & tools but you have to virtually dismantle the damn thing to do so - a long-winded process!
In the days when I used the Royal on almost every job, I always used to carry a cylinder as well, which meant I had the best vac for flat carpets and the best for upholstery, hard floors & stairs.
The bonus of a Royal is it makes an excellent back-duster for rugs. You wouldn't believe the amount of dry soil it can knock out of a rug. Sebo has almost no effect in comparison.
Solution used to sell them but I'm not sure if they still do, give them a shout