Unless your programs would benefit from tripple channel memory (couldn't tell ya
) you'll be fine with the 860. X58 also has better RAID configs as well I believe so unless you need either the 860 will do ya great.
The 860 and 920 perform about the same clock for clock (the 860 has higher stock clocks and turbo, making it slightly faster at stock, but they have the same OC headroom). You are really picking between the sockets, i7 860's 1156socket and i7 920's 1366socket.
The i5 is also a great CPU/deal (if you go 1156 socket) and is pretty much an 860 with no hyperthreading.