testing them and running them for days on end overclocked to the nuts are two very different things.
i would be hesitant to tell someone to expect more then 375 mh/s from a 5850 on average. A minor difference
from your 390 but it all adds up when discussing 5 of them. For every time a card hangs and it takes you time
to realize it and fix it.. has to be factored into your mining results.
just my opinion. i realize some 5850s perform better then others but a 990-1000 core clock speed, stable for days and day,
is impressive on these 5850 cards.
This should be pretty stable though because they run at 75c and it isn't a 990-1000 clock speed. It only requires 960 mhz these days to get 390 megahash. Plus these aren't some shitty brand they are sapphire cards.
i prefer to run at 940 at 375 mh/s, sapphire btw, for simple stability reasons.
if you got a good batch of cards more power to you!