Would it be best to use three separate pcie cables or use a 3 way splitter? Does it even matter? Would there still be equal power delivery with either option?
7900 XTX is 355W GPU. PCI-E 8-pin power cable is rated for 150W. You WILL melt the PCI-E 8-pin power cable if you split it 3-way at the end, just to populate all 3x 8-pin PCI-E connectors on GPU. That, and no PSU is able to deliver all 355W through single PCI-E 8-pin cable.
Use three dedicated power cables to power the GPU.