I came from xp pro 32bit to w8 pro 64bit upgrade on a new system and fresh install, absolutely fine, activated and upgraded with the media center add on key too. You need to run the upgrade assistant and buy on a 64bit os though for it to give you the 64bit download and create the install media on the 64bit os system. I only had my new machine when I did mine so I installed the release preview version for the 64bit os to do the buying and creating media. Then wiped release preview off, installed and activated xp, then booted from my created w8 install media and chose not to keep user documents etc to get a fresh install.
Get the latest drivers for w8 64bit from your mobo makers website and Intel. Also some of the mobo makers utilities and the latest bios.
The following sequence is based on my experience doing an MSI Z77A-GD65 build but for other mobo makers it should also broadly translate.
BIOS:
Update the bios if a newer one is available (also check mobo makers website for an even newer beta version if release notes are significant to W8 issues). If the newest bios still supports XP then reflash the bios prior to upgrading to W8, following mobo makers bios flash instructions. This may also update the option ROM's for LAN, RAID and the Intel Management Engine.
Drivers:
Intel Chipset (9.3.0.1021) - this I believe updated the support for USB3 without needing to update USB3 separately
Intel Management Engine (8.1.20.1337)
LAN driver
Intel VGA (9.17.10.2867) - optional, not required if using a discreet graphics card unless you want to use Virtu MVP but I found with Intel VGA 9.17.10.2817 that if I did this it would prevent Afterburner from unlocking voltage oc options.
Asmedia SATA driver (1.3.4.000)
Intel Rapid Storage - even though you may have supplied the driver during install for RAID, the larger Intel Rapid Storage package installs the utility, there's a package for if you're using RAID and one for AHCI.
Realtek High Definition Audio (6.0.1.6782)
Intel Rapid Start (2.1.0.1002) - optional, if you want to use a small partition on an SSD to enable fast hibernate, if so, you need to create a small partition equal to the size of system ram (8GB = 8192) and give the partition an id=84.
Intel Smart Connect (3.0.41.1571) - optional, if you want your computer to wake and fetch latest info such as your social network updates and emails.
Discreet Graphics Card - perhaps the latest beta drivers here
MSI Afterburner (2.3.0) - optional
Lucid Virtu MVP (2.1.115) - optional, if wanting to use both the iGPU and dGPU, this may stop MSI AB from giving unlocked voltage control
Utilities:
Fast Boot (1.0.0.8) - enables user to request next boot enters bios
OTP Service (1.0.004) - Over Thermal Protection (OTP)
Click Bios II (1.0.104)
Control Center (2.5.045) - this also enables the use of smart phone app to monitor system temps / oc
THX TruStudio Pro (1.04.03)
Super Charger (1.2.016)
Keyboard & mouse
Network Genie - optional, not appropriate for my board as it relates to the Realtek LAN chip and mine is Intel LAN but your board may have something similar
MSI Suite - optional, personally not keen so have left this off
MSI Live Update 5 - optional, personally not keen so have also left this off
Others:
Printer - HP have a new install wizard from their website which checks what it needs including software for OCR
At this point I'd re-enable windows auto update and run it to start applying all the important & critical patches.
If adding Windows Media Center I'd do it here and then rerun Windows Update to capture more important & critical patches.
Check Sean's SSD/HDD optimisation guide over on overclock.net and take / apply relevant tips
Tweak Start Screen, remove unwanted metro apps, bring metro apps up to date, choose most popular desktop applications to pin to start screen, possibly group into named groups.
At this point I'd create a drive image.
More installs:
Internet Security
Microsoft SkyDrive
Steam
GameSave Manager
Cloud backup
Office Suite
...
You may have a prob installing xp to modern hardware though unless you have xp with sp3 and may need the drive controller set to IDE, not AHCI in the bios. If your xp disc doesn't have sp3 on it you can use a free program called nlite to make a new one.
If you want to install w8 to raid 0 then it's best to get the intel rapid storage driver (floppy driver) before starting the w8 install and putting this driver onto a usb stick as you can provide this driver at the beginning of the w8 install process when you choose the drive / partition to install to.
Otherwise, you want to install using AHCI for the drive controller, this needs to be set in bios before commencing with w8 install, likewise for the RAID 0 option above you'd need to set it to RAID though.
I'd use a Microsoft account when asked and disable windows auto updates initially until after installing the latest drivers that you've sourced then I'd re-enable it.
Install drivers for chipset, lan, sound etc, run windows update a few times, do whatever tweaks such as some of whats in Sean's SSD/HDD optimisation guide over on overclock.net, when satisfied make a drive image.