BTW, Synergy is running a new kernal with overcloacking up to 1.9 GHz . . . and it provides great battery life.
The early Synergy builds didn't replace the stock kernal, so it probably gave battery life similar to stock. Early revisions of version 1.7 and version 1.6 and earlier ran the stock kernal. It was somewhere around revision 39 or so that a ziggy kernal was addded to Synergy version 1.7. They're at revision 66 as of today.
Synergy was also one of the first ROMs to get going on the S3. After getting a few versions under their belts and paving the way, Synergy has really become something desireable for a close to stock experience.
CleanROM is a ROM that's come along after Synergy came out. It's another close to stock ICS experience. What you'll see if you take a look at CleanROM's credits is some influence from the Synergy devs. CleanROM acknowledged them for the development of some features that were incorporated into CleanROM.
I've been running Synergy version 1.7 (skipped 1.6 and earlier) and I saw battery improvement over stock the moment I installed it. However, it's only gotten better with ziggy's kernal, so "horrendous" has never come to mind about the battery life in Synergy.
Synergy has also been very smooth for me. It's working very well and is very stable - no FCs on any apps I use and real smooth on the scrolling and page flips. It's this way without running it at an overclocked 1.9 GHz. I've kept it at 1.5 GHz for my max setting.
. . . and to parrot the response the op already got, yes there is a brightness slider under the dropdown toggels. However, I can't comment on music controls. I haven't considered using them on the lock screen.
This link will take you to the Synergy info, if you need it:
Synergy ROM