SO calculations/ predictions
261k/12 months=21,791 for each month available for all countries, subdivided into each EB1/2/3 category with 28.6% and then applying 7% country quota.
Vertical = EB GC SO = EB4+EB5 unused => EB1 unused => EB2 ROW unused => EB2 Most backlogged => EB3 ROW unused => EB3 Most backlogged
Horizontal= 121k SO / 12 months is 14580/month, EB 1/2/3 get 4170 visas per month 28.6% each category. Since, EB2I is most backlogged(as all countries are current) each month EB2I gets 4170 visas from FB Horizontal SO.
When EB1I gets current all VERTICAL SO will go to EB2I.
EB3I will be backlogged due to massive downgrades(after May2011 PD). With no vertical SO and less Horizontal SO in comparison with EB2I as other countries in EB3 Category will share FB SO as other countries does have EB3 backlog.
Nov visa Bulletin is just clearing EB1I and EB1C backlog. SO or rapid movement will take effect and be allocated to EB2I in coming months.
If Uscis intent is right, 150k out of 261k visas will be allocated to EBI1/2/3 by Sep2021. Prediction EB2/3 will be around Dec 2012 and Sep 2011 respectively by Sep 2021.