If I am replacing a PSU, I like to connect the mobo and SATA cables first and route them to the place where the PSU will be. Then I route the PCI-E cables for the GPUs, install the PSU in place and connect everything to it. Finally, I install the cards and plug the PCI-E cables to them. This is just how I like to do it (and it is convenient in my current setup) but there are other ways .
Excellent. My case has a good back panel where the current PSU cables are routed and it's very tidy. Hopefully i'll make it clutter free. Seems as though routing the cables tidily is the most time consuming part.