I have my system on a 60GB SSD, including all programs, swap file, temp files, etc. I put my ‘documents’ and assorted ‘libraries’ on another drive (too big) The Vegas temp files and undo files are on the SSD. I don’t even remember what system lag time is about. (read sweet!).
Put all of your Project media (assets) on a fast drive, make your output to the slower drive. You will not have a bottleneck. Figure it this way: When you copy a two gig file from a fast to a slow drive and it takes 5 minutes, on the day that Vegas renders the same file in less time, then you will have performance issue. I don’t think Vegas is going to out pace an external drive just yet.
Just my two-cents,
Jeff
http://www.narrowroadmedia.com