Just aquiring some bits! I've managed to get hold of a 6" inline fan for my intake and i've also ordered an air cooled shade. I'm going to replace my 4" intake with the 6" as you suggested. I'm also planning on using my old 4" intake to cool the shade. I've cut two holes in the roof of my room, one for the 4" inline fan which is going to blow air through the shade and back out of the other hole, hopefully isolating the heat of the HPS from the room.
Yes Swede, that lot should work great man, that setup should be better than mine, i want one of those air cooled shades myself, cant wait to see your setup in action, all the best man ;)