So a few things on this:
UEFI hastens boot because the firmware is more efficient. It doesn't really affect OS bootup speed, but affects the overall bootup speed of the PC from power-on. You don't have all of these add-on BIOS's in UEFI, like your AHCI BIOS, management engine BIOS, etc. All of that is included in an extremely fast UEFI. Microsoft is talking up NATIVE UEFI too, not the "Hybrid" UEFI that you get on non-current boards and such. Those types of firmware have a conventional BIOS, with UEFI boot extensions - usually just to support 2.2TB+ hard drives. It's not the same. Some companies have already sped up their BIOS's though. Some HP notebooks have an extremely fast BIOS that POST's in under 2 seconds. The other speed increases you get are with SSD's, but I timed Windows 8 with fast bootup (new hibernated-kernel Shut Down) and on an Atom 330 ION system with 4GB of RAM and a slower WD Blue 320GB 2.5" 5400RPM hard drive, it took about 12 seconds to load Windows after the relatively slow BIOS on that board. That's far faster than Windows 7. Full restart was slower than shutdown, but still faster than Windows 7 restarting.
Also, if you use Windows 8 and turn off the Start Screen, you just don't get it. The whole point of this release is to make the system and platform simpler from the ground up. You have the desktop there, sure, but if you turn off the Start Screen, you just have Windows 7. The entire platform is designed to be uber-simple across the board. More like an iPad, but it's a full PC. Consider the "Mom-factor" with the iPad. You can give your Mom an iPad and she can pick it up and use it pretty much right away without any real computer knowledge. Microsoft wants that simplicity for the PC. Apple doesn't quite get that yet with their computer systems, but everybody expects iOS to supplant OS X on Mac computers eventually, probably by the time they run out of 10.x numbers.
Also, if you like Windows 8 as a tablet OS, consider this: buy a tablet, buy a dock, hook up a full keyboard, mouse, and monitor to that dock, and you have the ultimate mobile PC that's also a fully-functional desktop. It's more mobile than a notebook because you can actually operate the thing while standing or walking around. Try to do that with an iPad - it just doesn't work. The whole purpose of technology is to make manual tasks simpler. If you don't like Windows 8, you don't like technology.