I would not shop the absolute best price on each component. Doing so will VASTLY complicate your aquisition/build process and add much time and shipping to your project timeline.
I (wisely) advise you to find a single vendor, for all functional components, if at all possible. Simplifies deliveries. Centralizes parcel tracking. Leverages deals and combos and simplifies rebate procedures. RMAs are to and from a single source. Personal and credit data are not "strewn" all over the global internet. Far less complicated and confusing, overall (K.I.S.S. ! ). Also, less finger-pointing if things don't work together.
Yeah ... Find a solid vendor that you trust with your personal and credit data and who has large volume and a long history of paradigm service ... I'm thinkin' newegg or tigerdirect, if you are in the states. Maybe Dell or some of the larger brick-n-morter "big-box" component sellers.
Regarding the differences between 920 and 930... aside from the obvious frequency/multiplier bump, I've read from multiple accounts of higher OC potential at similar voltages. The real life game/application difference will probably be marginal, but I say it would warrant the $10 premium for the newer tech. But since you can supposedly get an 920 for "$50 cheaper," then that's all you .