It is now widely known that the socket 1156 of intel's current line-up will be the first one to go.
Hence the 930 is your best choice, since 1366 is rumoured to be around for longer than 1156.
I don't know about i9. The only thing I can tell you is that there were much speculations about Intel's latest hexacore to be called i9, but it came to be known as i7-980X. And yes, it too runs on 1366.
I'm putting together a new machine and did this research. I'm going with the 930. It's just a few dollars more and it runs at 2.8GHz. You can overclock it to 3GHz easy. Several places I've read users overclocking to 4GHz. That's way more than I need, but the fact that many are doing it says a lot.
I've also read that the 1366 will be the longer life socket. That's really a mute point to me...I typically buy my MB and CPU as a set...and for that matter, when it's time for a new CPU/MB combo, I just build a new system...not that often mind you.
My reasoning is to wait a bit longer and upgrade all the tech to the (almost) latest out there at that time. So I buy 2nd best to get much better pricing and then get bigger drives, faster GPU, etc at the same time.
W/o a budget being given ......if < $1,200 I'd go with an 1156 based system. If you can go $1,450 or more, I'd do a 1366 based system. Below $1,000, I'd use AMD.
An i7-930 1366 chipset build gonna cost you $1,465 w/ all top end components. This build is expected to perform well with serious OC's (4.2 GHz and future upgrade to twin GFX cards)....Upgrade to Prolimatech Megahalems Heat Sink (extra $30 + fans) if ya wanna do 4.0 Ghz+