I have a 930, the only difference from the 920 is multiplier, but to get a 4GHz overclock or more you'll probably want to lower the multiplier so you don't stress your RAM too much. I'm running a 19x multiplier which a 920 can do easily (it is a 20x, the 930 is 21x maximum, add 1 to each if you use the Turbo speed).
My i7 build (i7 930, $209 Gigabyte motherboard, $170 OCZ Gold RAM, $80 WD Black HDD, $100 Antec 900 case, $100 Antec EA650 PSU, and $420 RadeonHD 5870) cost about $1400 total. If you want a good i7 920/930 build you'll have to spend more than $1000. If you really want the 930 build save up some more cash first. Otherwise go with the AMD X6 platform, it has 6 cores and AMD's chips are more cost effective.
The other thing that I'll continue to stress is the ASUS P6X58D is overpriced and not all that special. My Gigabyte X58A-UD3R cost $209 ($100 less than the P6X58D) while having nearly identical features. To add to that, the Gigabyte has MORE USB ports, MORE SATA ports, MORE Firewire ports, and added eSATA ports. It also has IDE and FDD connectors for legacy devices. I see no reason to buy the ASUS over what I consider to be a superior board for much less. I have the X58A-UD3R and have had no problems overclocking with it (running my 930 at 4.122GHz using a 217x19 multiplier, 1.29Vcore). It's a solidly built board with high quality components and a good cooling setup.
Newegg.com - GIGABYTE GA-X58A-UD3R LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX Intel Motherboard