Here is how arrived at the 10K figure. The rough assumption per month is 3K instead of 2.5K and since the later half of July had some people already in the system I just added 1K instead of 1.5K.
Now Spec's compilation is definitely a great compilation I probably cannot come even close in terms of class and caliber. Let’s discuss some of the assumptions in that compilation, Spec has himself suggested that these assumptions need
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60% EB2 PERM Certifications - If we compare the Jul 2007 inventory figures the ratio is higher than 66%. People who filed in EB3 post Jul 2007 have already ported to EB2, so now when the actual filing time comes it won't be a surprise if EB2 to EB3 is 75% especially for Jul - 2007 to Dec 2007. Remember at this time there were no issues with both labor and I140. 75% may look huge but it is probably closer to reality assuming someone had 0 years of experience in 2007 and had a PD of around this time now everyone has 5 years. There is no way by which these people could be accounted for in any porting calculations because they are not in the inventory. I just met a colleague his EB3 PD was Sep 2007 however he ported to EB2 recently so these are the kind of cases that will appear suddenly.
2.05 dependent ratio - We should assume that almost everyone with that kind of PD would be married (Parents in I/C do not allow that kind of freedom

- Now with this factor it would mean that only 1 in 20 families have a non USC kid, I would assume that that probably this is like a 1 in 4 case so the factor should be atleast 2.25.
- 20% I140 denial rate is fine but 85% of 2007 people remaining are slightly liberal but let’s carry them over.
Now with just these 2 factors skewed up following is the result.
8600 * (2.25/2.05) * (75/60) = 11798.
Just by slightly modifying the 2 factors slightly we arrive at 11.5K, so 10K really is a centrist value in that regard. In all my calculations I have always maintained 3K as the density for the later half of 2007 come 2008 this definitely comes down to 2.5K and then 2K.