I would say horizontal. I would also ditch the Intercooler, it's not the greatest design as far as cooling goes, putting fans on top of other fans isn't a great idea to begin with, and the Intercooler's puny fans barely put out any air compared to what the inside fans can. The power connection was never an issue after the EX series though, the problem was the original Intercoolers had plastic plugs that sometimes shorted out. Power drain isn't an issue though, I ran an Intercooler EX and 203W console off of a plug-modded 175W brick and it ran fine without problems. With the extra power of a 203W brick, I don't see how the Intercooler's power draw would ever be a problem. The problem is in the design. If it attached to the side (intake) vent instead of the back and blew COLD air INTO the console it'd be good.
I say horizontal because the main intake vent is the side (gray) one. If you use that as the base then that vent is completely blocked, leaving only the smaller top and bottom vents exposed. The hard drive side has a small vent but the DVD drive blocks most of it inside the console. The vents on the bottom are mostly blocked by the metal frame and motherboard (frame has holes in it but motherboard doesn't) and the top vents have to go through the frame as well. The side vent has to go through the frame too but it is big and allows a lot of air to flow.
