Looking for help to improve kH/s/W.

Here's my setup:
MSI Z68MA-ED55 (B3) motherboard
Intel G530 processor
4GB DDR3 1066 RAM
7950 Sapphire 100352-2L (purchased March 2013, voltage unlocked!)
16X-16X riser cable
Corsair TX750W power supply
AMD 13.1 drivers
AMD SDK 2.8
cgminer 2.11.3 (-I 20, --tc 22400 -w 256 -g 1 -l 1)
Sapphire Trixx

Best settings: 925/1250/.962V 560kH/s 3.29 kH/s/W.

Given high electricity cost my goal is to maximize kH/s/W.

My current best setup is 925/1250 at 0.962V for 560 kH/s at 170W or 3.29 kH/s/W, after many hours of systematically mapping gpu clock (850-1250), memclock (1250-1750), and gpu v (0.900-1.250). I've had the rig up to 740 kH/s stable (1225/1750/1.250V) but at 345W or 2.14 kH/s/W the efficiency just isn't there (would be great for a free power situation!).

Looking for advice from the experts on what to do next to improve my efficiency.

Thanks,

Tejsei