Tom, it's a bit late to spot this I suppose, but I think there has been a BIG oversight here. Take a look at the Lian Li product page for the PC-O7. The PSU bracket is clearly lower in the product photos than it is in your review sample, by about an inch. Also, the comment you made about the PCI riser cable only reaching the lower slot reminded me of a review I'd seen elsewhere which had the same problem, but it was said to be due it being pre-production and all production models would be shipped with the longer cable.
Anyway, if that gap between the PSU and top IS indeed bigger in the production version of the PC-O7, it would make watercooling easier and allow for a thicker rad up top possibly.