I have no experience with wireless PCI adapters, but I would highly recommend a USB adapter. If you choose to go the PCI route, I would probably opt to add an external antenna, which would make up for the inherently poor placement of the default attached antenna. I personally use exclusively USB adapters because 1) all my pci slots are taken 2)I like the flexibility of being able to move the adapter to another computer quickly and easily.
I use the netgear MR814 as well. I need the signal to go several hundred feet through lots of walls and doors, and I found that a higher gain, directional antenna improved the signal tremendously.