The Intel build is more powerful.
The X79 chipset doesn't have SATA AHCI drivers for 32-bit XP (but does for Vista and x64 XP); luckily, the Asus Sabertooth X79 motherboard has a Marvell SATA controller which does have drivers for 32-bit XP and provides two ports. Set the Intel (chipset-provided) SATA ports to IDE mode (to connect a disc drive for example) and use the Marvell ports for hard drives.
Marvell controllers have 2 .sys files in the same .inf file for the driver: 1 for the shared library, and another for the actual driver file. nLite cannot recognize this, and would only copy the shared library (mvxxmm.sys) without copying the actual driver. To avoid BSOD, after the text mode phase of the setup, boot into WinPE and manually copy the other .sys file to \WINDOWS\system32\Drivers, and then reboot into the graphics phase of the setup.
Other X79 motherboards: (non-exhaustive list)
According to this PDF, Haswell doesn't have SATA or Audio drivers for XP. ASUS SABERTOOTH X99 doesn't have any drivers for XP or Vista on ASUS' official website. So I'd consider X79 + i7-4960X to be the best officially supported build.
If compatibility with the onboard Intel SATA controller on XP is desired, see Windows 2000 builds.
There's an overclocking report of an i7-6950X running XP. No idea if modded drivers are available for such a build.
Other 990FX motherboards: (non-exhaustive list)
The Nvidia GPU is more powerful.
The last driver version to support XP is 368.81 (x86, x64), or 355.60 (x86, x64) for the GTX TITAN Z. The last driver version to support Vista is 365.19 (x86, x64).
It's possible to modify the 368.81 driver to add support for later 9xx series of GPUs, as well as the GTX TITAN X.
Therefore, without driver modification, the most powerful GPUs usable on XP are: GTX TITAN Z, GTX TITAN Black, and GTX 780 Ti, in this order. (TITAN GPUs are high end, so ordinary users might not want to pay such high price.)
Different websites rank the three cards differently, but all websites I've seen seem to agree that the performance is similar. Since GTX 780 Ti would be the cheapest out of these three most (if not all) of the time, it should be the card of choice.
With driver modification, the GTX 980 Ti and the GTX TITAN X can be used. These are more powerful than the GTX TITAN Black, but less powerful than the GTX TITAN Z. Similarly, the GTX Titan X might be more powerful than the 980 Ti, but is too expensive for not much gain.
Honorable mention: GTX 960, which is one generation newer, but not more powerful, than GTX 780 Ti. The 9xx series is the last generation of cards to be supported by the 368.81 driver. Due to being newer, it supports hardware decoding of VP9.
Radeon 200 series stopped supporting XP mid-way. The last GPU that supports XP with normal drivers is R9 270X, but it's less powerful than HD 8990, the best card from the previous series.
However, there is an iCafe driver for XP that supports R9 280X, which is more powerful than HD 8990.
The last Sound Blaster sub-series to have Windows XP and Vista drivers is X-Fi.