My MSI's documentation is also really good. Any upstanding motherboard manufacture will have pin layouts, dimm layouts, where your power draws, if there are any buttons what they do where and how.
Yea SSD's are getting to be amazing now, the price difference might not be a big enough drop to go down from 250GB to 120GB, and it's not just programs that need to be installed, so having the extra space is probably a smarter idea if the price difference is not that high.
Yea Derek, PCIe is super fast. I've seen HDD's hooked up through PCIe and they are blazing fast, SSD's should be more. I haven't checked if the price is coming down, but as far as I know you don't need a special drive, just the bracket which replaces the sata, and power like usual.