I figured it was time for me to post since I can't figure it out after trying for quite some time.
I have two Diamond 7970s and I'm using the following .bat:

setx GPU_MAX_MEMORY_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
--gpu-engine 1010 --gpu-memclock 1440 -I 12 --lookup-gap 2 --thread-concurrency 4096 -g 2 -w 512

It's giving me 225Kh/s. If I bump -i to 13 I get tons of HW errors. I've tried setting TC to 8192, 8191, or 8193 as others have said and it gives the this error:

Maximum buffer memory device 0 supports says 536870912
Your scrypt settings come to 1073610752
Error -61: clCreateBuffer (padbuffer8), decrease TC or increase LG

I've also tried setting -g to 1 or 3 and neither is better.
Tried playing with -w and nothing better

Anyone have any ideas?