Bob,
I see you are dividing total points by "calendar days" which doesn't really reflect what the machines are producing due to varying amounts of run time per calendar day caused by the validation process and WU reporting timing. A more accurate calculation is the average number of points per hour of runtime.

For the 920:

962.01 hours of CPU time
159,843 total points
Average points per hour of runtime 166.16
Multiply by 192 to get a theoretical "perfect" calendar day with 8 days of CPU run time 31,903 ppd.

For the 860

1091.7 hours of CPU time
166,035 total points
Average points per hour of runtime 152.09
Multiply by 192 to get a theoretical "perfect" calendar day with 8 days of CPU run time 29,201 ppd

Looking at these numbers, the 920 is outperforming the 860 by about 9%.