Other than the processor and the mobo, what are the other components you've decided on?
It's a similar situation as in a recent thread by Tank. Like I said there, the Nehalem is definitely better for bragging rights. Else, the Lynnfield may be the better bang for the buck.
Tough choice. However, the LGA1366 is probably the best platform in the market right now. Also there is the matter of the triple channel memory controller. I personally like it more.
Again, the 860 runs a cooler and has lower power consumption.
So in my opinion, if the price difference between the 920 Vs 860 build isn't too much, go ahead with the 920. Actually if you're considering the LGA 1156, I'd only recommend the i5 750.
I think if that ASRock board is a good one, then you're getting excellent value for the 920 build.
All the best my good man.