But they are still two completly diffrent computers, the UDOO x86 is a true x86 PC, I mean with standard CELERON/ATOM processor 2Ghz+ and 2-8GB RAM and Gigabit Ethernet/SATA, so there is no point to compare it with RasPi "how they've performed in comparison" but this is only my point of view.
I think you'd better look at UDOO x86 from a different angle, as a "classical" PC Notebook's motherboard based on Intel Atom but with an onboard Arduino based microcontroller providing many I/O and by the way this product is only Pre-Order so not publicly available so I guess you'll not find a lot of people that tried it for now, the reviews you saw on Youtube are certainely pre-production sent to reviewers for a bit of "free" advertisement.
And there is also a huge processor difference between the low and high-end models (I suppose the reviews on Youtube are based on the top model ;-) between small Atom X5-E8000 2.00 Ghz and better Pentium N3710 2.56 Ghz (and N3710 processor is what you have in many 250$ low budget Notebooks), same for RAM with 8GB for higher priced model vs 2GB for cheapest one.