I've been building for 14 years now, so decided to just go for something a bit more unique and try out custom watercooling.
Hardline is almost as hard as everyone says it is, but isn't impossible. Prepare to spend about 15 minutes per bend if it's your first time (It was mine). The kit from Thermaltake works wonders, just be careful of burrs on the tubing after you cut the bevel using the reamer. If you're picky about a smooth cut, a Dremel will work better if you have a steady hand, or better yet a router table if you have access to one (but this may just be overkill).
Speaking of bevel, EK highly recommends a 45 degree outer bevel on the hard tube. This should be a requirement, as it's almost impossible to put a tube without a bevel into the fitting without damaging the inner O-ring.
You CAN fit an EATX into a Core P5. But you will need taller motherboard standoffs. I ended up screwing 3 standoffs into 1 for each hole. This is to clear all the cables as EATX will cover the passthroughs. Keep in mind that this means that you MUST mount your PCIE devices vertically, so don't do this if you have multiple PCI-E cards.
Everything else went pretty smoothly, and the rig runs silent and cool. AMD's PBO will turbo all cores to 4.15GHZ happily with 250W as the power limit. With a beefier PSU, I would have maybe pushed harder... but that's for another day.
Overall I'm very happy I did it, but it's definitely not for the faint of heart... Or the impatient :D