I did a quick benchmark with regards to the difficulty ratio between chain lengths. I used the CPU miner in my Primecoin High Performance wallet (latest HP14 release). It allows targeting different chain lengths using the -sievetargetlength parameter.


So 11-chains should be about 28.7 times harder to find than 10-chains. So that number is definitely closer to 30 rather than 10. Sunny King originally assumed that the ratio would be about 32. Also note that the ratio keeps growing as the chain length increases.

I also compared these numbers to some earlier benchmarks. It seems that the ratios are smaller with more optimized code. So my guess is that for GPU miners the ratios may be slightly smaller. (Anyone want to confirm that?)

My network charts page at http://xpm.muuttuja.org/charts/ tries to estimate the total network computation power in terms of chains per minute. It shows that chains/min peaked at 20 chains/min on May 13th, which is definitely not enough to push difficulty above 11. Last December we actually needed about 40 chains/min to go above 10.

Currently the network is mining at about 8.5 chains/min, which is equivalent to about 1500 GPUs mining at 8.2 chains/day.