For the audio sync issue, I'd double check your audio/video codecs. I always use CCCP. http://www.cccp-project.net/
Check if the Intel HD 2000 video supports DXVA hardware acceleration. (should since it's fairly new) http://en.wikipedia.org/wiki/DXVA I Had the same choppyness issue when...
I stream BR Rips from a gigabit network share RAID5 (Seagate 2tb 5,900rpm drives) and have no issues with lag. I'd say go WD Green or the Seagate Green.
Unless you're doing huge amounts of I/O for video file compression or something like that you won't see any performance increase in going...