How to calculate the diff of

1000 sol/s = diff ?

difficulty is about setting target, if pool have good share calculating system then in theory doesent matter what difficulty you get, because when you get higher target you findig harder shares but you get mor pay for them so it would be the same as finding lower shares faster.... but there are 2 aspects - with higher diff pool will have less work checking your share, but can be that you will not find last share before start new job, when with lower you still could find a part of value, with to low diff your miner, connection and pool would choke to death...
I belive for 1000 sol/s 4096 diff would be best ... (value of one share would be 4096x of value with diff of 1 ?)