I will fill in some of the frequencies above...I found a few googling around.
Take a look at BitMain's own undercloaking post.
It will give you an extra edge on down clocking and down volting.
It uses variable POTs to control voltage to the ASICs.
The Resistors adjacent to the DC-DC converter need to be removed and attach a pot there.
You need 1 pot for each DC-DC converter. The pot can be obtained from local market or ebay.
Pencil mod will also work but with a little effort I recommend Bitmaintech's own hardware hack method especially if you are a Do-It-Yourselves guy.
I will post the link to that post.
You can do it yourselves or can get help from any DIY guy or an electronic repair shop.
Update: Here is BITMAINTECH official undervolting/underclocking post https://bitcointalksearch.org/topic/m.7031946