First thing is, not all 920's can get to 4.0ghz. Most probably will, but not guaranteed.
To try to get 4.0 you're going to need quite a bit of tweaking with your setup. Yes the ram is a little bit of a problem, but you might be able to get it stable anyway.
You will have to basically overclock your ram or under clock it. In this case overclocking might prove to be easier. The reason is, the uncore value should be around two times the ram frequency. If you pick the lowest ram setting, the nearest uncore is more like 3 times ram speed. You may or may not be able to get this stable that way.
The other option is to overclock the ram while keeping a nice 2 to 1 ratio with the uncore. You can try making the timings higher to help with the higher clocks.
BTW, I'm using BLCK of around 190 with turbo on for this, if you turn turbo off, you'll need 200 BCLK, and I'm not sure your ram will be able to do that.