There apparently no reason to rise the frequency higher than 400 without voltage rising. The hashrate will not increase heavily after 400.
But even if you will modify voltage, S5 will heating up too much, so my advice is not to do this without additional cooling mods (or without frosty air for intake...)...
i had one get to 412 and give me 1330gh all others like 393 or less
I changed out the fans for the SP120's. Those work well, but they can't keep up with overclocking. Don't want to burn up a unit, don't have the frosty air on tap tonight, conditions are not ideal. While working on this I cannot help but think a 2nd pull/exhaust fan would help a great deal. What's the consensus? Need to do some more research.
And I don't want to blow a bunch of money on fans after having put the SP120's in, which I wouldn't change for a second. The sound reduction is ahhhmazing.
Starting from where I am, 2 machines with SP120's added, what would you do for cooling?
Have two basic ideas which would give some options, as I have a third machine due soon.
1) Take one machine and install SP120's front and back. They are 4pin PWM, run them from the board.
2) Buy inexpensive 3 channel fan speed controller. Buy 3x 120mm fans that will spin well over 3k rpm and push over 140 cfm. Replace stock fans with the high RPM fans and run them from the controller. I hear static pressure is important, I also feel like there's no replacement for displacement.
If a push / pull setup is workable and does provide better cooling I can certainly go that way. Or, go raw power and deal with the noise.
If you read this far, and don't overclock or are interested... try setting 337.5M and take a look at your hashing speeds and utility numbers. BUT, please let me know about push pull fans, and what you would do given the same situation.