My question is however, with each card needing 2 water blocks for the the GPUs alone, will the built in PCI-E bridge chip need a waterblock too? Will this even be affected by the overclocking? Will there be enough space to squeeze something in between the 2 GPUs with water blocks on them?
No more so than any other crossfire setup so no. As for the OC, water cooling may buy you something on the GPU's but it will get very little in the way of CPU and chipset cooling. Water alone doesn't drop the temp enough get any additional headroom vs air with the current CPU/MB's out there.
Without knowing what type of block/s you would be using it's hard to say.
And of course I meant Q9550 @ 3.4 GHz to start with not 3.2... that number was left over from my look at the cheaper Q9450 Looking to creep it up towards 4GHz stability permitting.
Of course water drops the temp enough to do this, I don't really want to have something that sounds like a jet engine cooling the CPU and shifting the air inside the case so I can get more performance out of it.
Point is, normal crossfire setups don't have the plx chip, I'm talking about the x2 card, not 2 x the single gpu card.
I hadn't even investigated the exact water blocks yet, seems there's not much about for the 4870 either. So guess I'll wait for a full cover block, or a HIS card with water block as standard.