I have installed Xp64 successfully on many workstation class systems running core 2 quad or XEON. Typically i would install it only on systems of the LGA771, LGA1366 types
Some examples where i installed XP 64 successfully
Dell PRECISION Tower 690 ( LGA 771, with dual Xeon 3 GHZ processors)
Dell Precision Tower 5500 ( LGA 1366 , with solo Hex core Xeon X5670 ( but has 12 threads due to HT )
Lenovo Thinkstation S10 ( LGA 775, Core 2 Quad 9550 , no hyperthreading)
I use it pretty frequently as it has little bloatware , and as long as you can download correct drivers from the manufacturers website , you should not have any issues
boots pretty fast ( I'd suggest use SATA SSD for the boot partition ) and most importantly CAN access upto a whopping 128 GB RAM .
I also installed Office 32 bit and a few other 32 bit apps which run seamlessly , but 32 bit apps can only use upto 2 GB RAM
Dell Supported XP till 2013 models , so i worked ina company that had installed Xp 32 bit on intel core i 3rd gen ( COre i5 35XX) and dell had drivers for them .
If you really want to use it along with Windows 7 , id suggest installing it Before you install Windows 7 , otherwise it can get tricky .
There are downsides however , i and how it affects you is subjective
1. You need to configure your drives as SATA ( AHCI And Raid are problematic unless you have a way of customizing your install cd with proper drivers using nlite)
2. Some workstations i had to physically rewire the drive as SATA instead of RAID ( Precision 690 !)
3. Not sure if you still want to use Xp64 in 2016 now , but if you need to , i would suggest you get the Service Pack2 OEM Edition , as it has updated drivers
4. You certainly need to install .NET Framework 4.0 , but you have to download and install Windows imaging component first ( WIC)
5. Ensure you have downloadable drivers from the manufacturer for XP64 bit , otherwise it can be a gamble requiring you to invest more time to get correct drivers.
6. Officially Firewire audio is not supported, but firewire is supported for other applications
7, Does NOT support Microsoft services for unix officially , so if you want to use unix programming - you can dual boot with Ubuntu or RHEL
ONce installed Excellent support for legacy hardware like SCSI , Firewire ( including firewire based ethernet) , parallel and serial devices, floppies ( some scsi devices may need drivers )
Can run 32 bit windows apps without frequently hanging or crashing
Access upto 128 GB RAM !!!
As long as manufacturer drivers can be found , its preferable to Windows 7 for 64 bit PC's released between 2006 and 2010, but i cannot assure things will be fine in the future as XP is mostly dead now .
Dell precision 470
Dell precision X90 series towers
Precision X400 series towers/rack ( T5400, T7400)
Precision X500 series towers ( T5500, T7500)
Lenovo Thinkstation S10, D10
Dell optiplex 64 bit PC's : 960, 980 etc
Thinkcenter pcs with core 2 or core i 5/5 1st generation
you can realize advantage only if you mobo supports > 4GB or RAM , otherwise stick it to Win 7 32 bit , since no advantages if your RAM is hardware limited