Well I can say that the Dyson I have, bought from Lowe's and new in box, pulls up close to 100% of stuff in the carpet. If not 100%...at least 90%.
I do know that I can vacuum a spot until it "looks" clean, empty the canister, go back over that spot and pick up more dirt.
As for an Oreck, I worked on one that belonged to a lady that works with my wife, that had quit working altogether as well as lost suction. A wire had "burned" off of the main switch and the handle was plugged with hair and God knows what else.
I used it and other than being lighter in weight than the Dyson, I could not see that it picked up dirt any better.
I also have a 5 gallon shop vac that does really well and even use it to get into tight corners and under the couch.