to be entirely honest clock the C0 as high as you can and be done with it - you're not gonna notice 200MHz in real-world usage, so 4GHz is just e-peen.
If though you have trouble getting past 3.4 ish with your C0 then maybe look at upgrading, but there's no guarantee a 930 will get to 4GHz anyway.
Plus I doubt you'd get very much for a C0 920 anyway.
So I went with your advice and canceled my order on the 930. I overclocked the 920 C0 to 4.09 Ghz.
Did some prime testing
46 In use temps
89 Was my 100% Temp
Core Voltage is at 1.4
I had it at 1.2 with 3.4 Ghz so I guess .2 extra giving me 4ghz is nice. Seems stable.
I will get another CPU when it's necessary then. Thanks again.
update: For those who care. http://valid.canardpc.com/show_oc.php?id=1072596