With 4 cards : hashrate ~ 2,4 MH/s (Vcore:~1060 mv,GPU:~1035Mhz,MEM:1500Mhz)
Stale: ~ 5% (latency ~25ms) ==> valid hashrate = 2,28 MH/s
Power consumption : 910 watts
KH/watts : 2280/910 = 2,505 KH/w
You can see there no big difference between the two settings :
the first is a little more efficient, but the second achieve more hashrate.
you will have less stale with the first, resulting in less load on the pool.
Keep in mind that these settings has been tested on my card (all bought from the same batch)
and the perfect setting can vary a lot.
Reducing network and pool load
use no-submit-stale 1 in config
--no-submit-stale Don't submit shares if they are detected as stale