Define "heavy" is what you have to ask

. I can't even get a day out of mine.
Exactly!! Struggle with half a day with very heavy usage. I can get through a day but not a chance I cannot go without charging it that evening. See the details listed below of Darky's v9.4. that I copied.
Darky's v9.4 Extreme Edition
>> This is an evolution of v9.3 Extreme Edition.
>> The main goal is more stability and a faster system.
>> Refinements where possible.
Download
http://www.multiupload.com/FEPWSRSGGG
Changelog
Based on latest XWJS8
Faster UI, smoother experience.
Introducing Dark Voodoo Kernel
- Made by ficeto [Team Darky Dev]
- Based on Voodoo 5.5 [by supercurio]
- Voodoo Sound 5.5
- Usual Tweaks and Hacks like BLN etc.
- Rewritten Recovery [mount scripts, other more reliable scripts, new graphics, new UI]
- Reported very good battery life [3.5 days with heavy use]
- Speed of Voodoo, means: blazing speed
Included my RAM Hack Script [more free RAM and less lags]
Dozens of my new build.prop scripts [faster, more stable, better]
Reworked zipalign binary and scripts [faster startup, apps use less RAM // thanks Bo$s]
Cleanued up /system [sysctl etc.]
4 completely new Ringtones / Alarm Sounds and 1 new SMS sound [I spent more hours on those than on the ROM]
Speed Improvements for internal & external SD-Card // up to 1.5x speed [faster mediascanner etc. // thanks ickyboo]
Fixed Bluetooth A2DP Connectivity [thanks ickyboo and spoidar@xda]
New Bootanimation by Goldieking [best he has done so far! you'll be impressed...]
New HQ 960 x 800 Wallpapers I've custom collected
Disabled increasing ringtone [like it was in v9.2]
Changed call connect / disconnect sounds [Samsung default now]
Updated update-script
Implemented FuguTweaks for more speed [Gingerbread 2.3.3 smoothness]